Q.Compute $P(A|B)$, if $P(B) = 0.5$ and $P(A \cap B) = 0.32$.

Showing the 12 most recent of 30 on this concept.

1. TG EAPCET 2026Set eng-2026-05-09-FN1 markMCQ
   Q.If $P(A) = \dfrac{3}{8}$, $P(\overline{A}|B) = P(\overline{B}|A) = \dfrac{3}{5}$, then $P(A \cap B) + P(B) =$ (A) $\dfrac{21}{40}$ (B) $\dfrac{2}{13}$ (C) $\dfrac{3}{14}$ (D) $\dfrac{5}{12}$

   ›Reveal solutionSolution

   We use the given conditional probabilities to set up equations for $P(A \cap B)$ and $P(B)$, then solve and sum them. The result is $\frac{21}{40}$, which corresponds to option (A).

   We are told:

   • $P(A) = \frac{3}{8}$
   • $P(\overline{A} \mid B) = \frac{3}{5}$
   • $P(\overline{B} \mid A) = \frac{3}{5}$

   We need $P(A \cap B) + P(B)$.

   ---

   Concept and intuition

   Conditional probabilities like $P(\overline{A} \mid B)$ relate the probability of the complement of $A$ given $B$ to the joint probability $P(\overline{A} \cap B)$. Since $P(\overline{A} \mid B) = \frac{P(\overline{A} \cap B)}{P(B)}$, we can write an equation linking $P(B)$ and $P(A \cap B)$. Similarly, $P(\overline{B} \mid A)$ gives a relation between $P(A)$ and $P(A \cap B)$. This lets us solve for the unknowns.

   ---

   Step-by-step solution

   1. Use $P(\overline{B} \mid A)$ to find $P(A \cap B)$ By definition:

   $P(\overline{B} \mid A) = \frac{P(\overline{B} \cap A)}{P(A)} = \frac{3}{5}$

   Since $P(\overline{B} \cap A) = P(A) - P(A \cap B)$, we have:

   $\frac{P(A) - P(A \cap B)}{P(A)} = \frac{3}{5}$

   Substitute $P(A) = \frac{3}{8}$:

   $\frac{\frac{3}{8} - P(A \cap B)}{\frac{3}{8}} = \frac{3}{5}$

   Multiply both sides by $\frac{3}{8}$:

   $\frac{3}{8} - P(A \cap B) = \frac{3}{5} \cdot \frac{3}{8} = \frac{9}{40}$

   So:

   $P(A \cap B) = \frac{3}{8} - \frac{9}{40} = \frac{15}{40} - \frac{9}{40} = \frac{6}{40} = \frac{3}{20}$

   2. Use $P(\overline{A} \mid B)$ to find $P(B)$ By definition:

   $P(\overline{A} \mid B) = \frac{P(\overline{A} \cap B)}{P(B)} = \frac{3}{5}$

   Now $P(\overline{A} \cap B) = P(B) - P(A \cap B)$. Substitute $P(A \cap B) = \frac{3}{20}$:

   $\frac{P(B) - \frac{3}{20}}{P(B)} = \frac{3}{5}$

   Multiply both sides by $P(B)$:

   $P(B) - \frac{3}{20} = \frac{3}{5} P(B)$

   Bring terms together:

   $P(B) - \frac{3}{5}P(B) = \frac{3}{20}$

   $\frac{2}{5}P(B) = \frac{3}{20}$

   So:

   $P(B) = \frac{3}{20} \cdot \frac{5}{2} = \frac{15}{40} = \frac{3}{8}$

   3. Compute the required sum

   $P(A \cap B) + P(B) = \frac{3}{20} + \frac{3}{8} = \frac{6}{40} + \frac{15}{40} = \frac{21}{40}$

   Tip

   Notice that $P(A) = P(B) = \frac{3}{8}$ here — a nice symmetry that emerges from the given numbers.

   Watch out

   A common mistake is to treat $P(\overline{A} \mid B)$ as $1 - P(A \mid B)$ incorrectly — that works only if you adjust carefully. Always go back to the definition $P(\overline{A} \mid B) = \frac{P(\overline{A} \cap B)}{P(B)}$.

   ✓Final answer

   The correct option is (A).

   ANSWER: A

2. TG EAPCET 2025Set eng-2025-05-02-AN1 markMCQ
   Q.A, $B_1$, $B_2$, $B_3$ are the events in a random experiment. If $P(B_1) = 0.25$, $P(B_2) = 0.30$, $P(B_3) = 0.45$, $P\left(\dfrac{A}{B_1}\right) = 0.05$, $P\left(\dfrac{A}{B_2}\right) = 0.04$, $P\left(\dfrac{A}{B_3}\right) = 0.03$, then $P\left(\dfrac{B_2}{A}\right) =$ (A) $\dfrac{6}{19}$ (B) $\dfrac{8}{19}$ (C) $\dfrac{12}{19}$ (D) $\dfrac{5}{19}$

   ›Reveal solutionSolution

   This is a classic Bayes’ theorem problem: we are given prior probabilities for three mutually exclusive events and the conditional probabilities of A given each, and we need the posterior probability of $B_2$ given A. The answer is $\frac{6}{19}$, which corresponds to option (A).

   We start with the concept: Bayes’ theorem lets us “reverse” conditional probabilities. Here, we know $P(A \mid B_i)$ and want $P(B_2 \mid A)$. The key is that the $B_i$ form a partition of the sample space (they are the only possible “causes” of A), so we can compute $P(A)$ using the law of total probability, then apply Bayes’ formula.

   1. Identify the given data

      • $P(B_1) = 0.25$, $P(B_2) = 0.30$, $P(B_3) = 0.45$
      • $P(A \mid B_1) = 0.05$, $P(A \mid B_2) = 0.04$, $P(A \mid B_3) = 0.03$ The events $B_1, B_2, B_3$ are mutually exclusive and exhaustive (their probabilities sum to 1), so they form a partition.

   2. Compute the total probability of A

      By the law of total probability:

   $P(A) = P(B_1)P(A \mid B_1) + P(B_2)P(A \mid B_2) + P(B_3)P(A \mid B_3)$

   Substitute:

   $P(A) = (0.25)(0.05) + (0.30)(0.04) + (0.45)(0.03)$

   Calculate each term:

   • $0.25 \times 0.05 = 0.0125$
   • $0.30 \times 0.04 = 0.0120$
   • $0.45 \times 0.03 = 0.0135$ Sum:

   $P(A) = 0.0125 + 0.0120 + 0.0135 = 0.0380$

   3. Apply Bayes’ theorem for $P(B_2 \mid A)$ Bayes’ theorem states:

   $P(B_2 \mid A) = \frac{P(B_2) \, P(A \mid B_2)}{P(A)}$

   Plug in the numbers:

   $P(B_2 \mid A) = \frac{0.30 \times 0.04}{0.0380} = \frac{0.0120}{0.0380}$

   4. Simplify the fraction Divide numerator and denominator by 0.002 (or multiply by 1000 to clear decimals):

   $\frac{0.0120}{0.0380} = \frac{12}{38} = \frac{6}{19}$

   So $P(B_2 \mid A) = \frac{6}{19}$.

   Tip

   A common pitfall is forgetting to compute $P(A)$ correctly — students sometimes use only the numerator. Always check that the denominator is the total probability of A, not just one term.

   ✓Final answer

   The correct option is (A).

   ANSWER: A

3. TG EAPCET 2021Set eng-2021-08-04-FN1 markMCQ
   Q.If $P\left(\dfrac{A}{B}\right) = \dfrac{3}{10}$, $P\left(\dfrac{B}{A}\right) = \dfrac{4}{5}$ and $P(A \cup B) = K P(B)$, then $\dfrac{1}{K} =$ (A) $\dfrac{40}{49}$ (B) $\dfrac{40}{43}$ (C) $\dfrac{100}{101}$ (D) $1$

   ›Reveal solutionSolution

   The key idea is to use the definitions of conditional probability to relate $P(A \cap B)$ to $P(A)$ and $P(B)$, then express $P(A \cup B)$ in terms of $P(B)$ alone. The result is $\frac{1}{K} = \frac{40}{43}$.

   We are given two conditional probabilities and a relation involving the union. The goal is to find $\frac{1}{K}$, where $P(A \cup B) = K P(B)$. This is a problem about linking conditional probabilities to the basic probability of events, so we start by writing down what each conditional means.

   Recall: $P(A/B) = \frac{P(A \cap B)}{P(B)}$ and $P(B/A) = \frac{P(A \cap B)}{P(A)}$. These are not symmetric — each gives a different ratio. Our job is to use them to find $P(A)$ and $P(A \cap B)$ in terms of $P(B)$, then compute $P(A \cup B)$.

   1. From $P(A/B)$ we get $P(A \cap B)$ in terms of $P(B)$.

   $P(A/B) = \frac{3}{10} \quad\Rightarrow\quad \frac{P(A \cap B)}{P(B)} = \frac{3}{10}$

   So

   $P(A \cap B) = \frac{3}{10} P(B).$

   2. From $P(B/A)$ we get $P(A)$ in terms of $P(A \cap B)$.

   $P(B/A) = \frac{4}{5} \quad\Rightarrow\quad \frac{P(A \cap B)}{P(A)} = \frac{4}{5}$

   Hence

   $P(A) = \frac{5}{4} P(A \cap B).$

   3. Substitute the expression for $P(A \cap B)$ from step 1 into step 2.

   $P(A) = \frac{5}{4} \cdot \frac{3}{10} P(B) = \frac{15}{40} P(B) = \frac{3}{8} P(B).$

   So $P(A)$ is $\frac{3}{8}$ of $P(B)$.

   4. Now write $P(A \cup B)$ using the inclusion-exclusion formula.

   $P(A \cup B) = P(A) + P(B) - P(A \cap B).$

   Substitute the expressions we have:

   $P(A \cup B) = \frac{3}{8} P(B) + P(B) - \frac{3}{10} P(B).$

   5. Combine the terms over a common denominator. The denominators are 8, 1, and 10. The LCM is 40. So:

   $\frac{3}{8} = \frac{15}{40},\quad 1 = \frac{40}{40},\quad \frac{3}{10} = \frac{12}{40}.$

   Therefore:

   $P(A \cup B) = \left( \frac{15}{40} + \frac{40}{40} - \frac{12}{40} \right) P(B) = \frac{43}{40} P(B).$

   6. Compare with the given relation $P(A \cup B) = K P(B)$. We have $P(A \cup B) = \frac{43}{40} P(B)$, so $K = \frac{43}{40}$. Hence

   $\frac{1}{K} = \frac{40}{43}.$

   Watch out

   A common mistake is to treat $P(A/B)$ and $P(B/A)$ as if they were the same, or to forget that $P(A \cap B)$ appears in both but must be expressed consistently. Always write the definition first.

   ✓Final answer

   The value is $\boxed{\frac{40}{43}}$, which corresponds to option (B).

4. TG EAPCET 2026Set eng-2026-05-10-AN1 markMCQ
   Q.A card is drawn randomly from a well shuffled pack of 52 cards. If A is the event of getting a diamond card and B is the event of getting an ace card, then the probability that exactly one of the events among A and B to occur is (A) $\dfrac{15}{52}$ (B) $\dfrac{4}{13}$ (C) $\dfrac{17}{52}$ (D) $\dfrac{5}{13}$

   ›Reveal solutionSolution

   The probability that exactly one of the events A (diamond) or B (ace) occurs is the sum of their individual probabilities minus twice the probability of both occurring. The result is $\frac{15}{52}$, which corresponds to option (A).

   We want the probability that exactly one of the two events happens — that is, either we draw a diamond that is not an ace, or we draw an ace that is not a diamond. This is a classic "exclusive or" (XOR) situation.

   Why this approach works:

   If we simply add $P(A) + P(B)$, we count the case where both occur (the ace of diamonds) twice. To get exactly one, we subtract that double-counted overlap once more than usual — hence $P(A) + P(B) - 2P(A \cap B)$.

   ---

   1. Identify the probabilities of each event individually.

      • There are 13 diamonds in a deck of 52, so $P(A) = \frac{13}{52} = \frac{1}{4}$.
      • There are 4 aces, so $P(B) = \frac{4}{52} = \frac{1}{13}$.

   2. Find the probability that both events occur (the intersection).

      • Only one card is both a diamond and an ace: the ace of diamonds.
      • So $P(A \cap B) = \frac{1}{52}$.

   3. Apply the formula for exactly one event.

      • Exactly one of A or B occurs means: $(A \text{ and not } B)$ or $(B \text{ and not } A)$.
      • The probability is:

   $P(\text{exactly one}) = P(A) + P(B) - 2P(A \cap B)$

   • Substitute the values:

   $\frac{13}{52} + \frac{4}{52} - 2 \cdot \frac{1}{52} = \frac{13 + 4 - 2}{52} = \frac{15}{52}$

   4. Check against the options.
      • $\frac{15}{52}$ matches option (A).
      • For completeness: $\frac{4}{13} = \frac{16}{52}$, $\frac{17}{52}$, and $\frac{5}{13} = \frac{20}{52}$ are all different.

   Tip

   A quick sanity check: The probability of exactly one is also $P(A) + P(B) - 2P(A \cap B)$. Many students mistakenly use $P(A \cup B) = P(A) + P(B) - P(A \cap B)$, which gives "at least one" instead of "exactly one."

   Watch out

   A common pitfall is forgetting to subtract the intersection twice. If you only subtract it once, you get $\frac{16}{52} = \frac{4}{13}$, which is option (B) — the probability of at least one, not exactly one.

   ✓Final answer

   The correct option is (A).

   ANSWER: A

5. TG EAPCET 2025Set eng-2025-05-02-AN1 markMCQ
   Q.Let $P = \begin{bmatrix} 1 & 2 & 3 \\ 4 & 5 & 6 \\ 7 & 8 & 9 \end{bmatrix}$ be a matrix. Three elements of this matrix P are selected at random. A is the event of having the three elements whose sum is odd. B is the event of selecting the three elements which are in a row or column. Then $P(A) + P\left(\dfrac{A}{B}\right) =$ (A) $\dfrac{221}{420}$ (B) $\dfrac{17}{21}$ (C) $\dfrac{21}{20}$ (D) $\dfrac{3}{2}$

   ›Reveal solutionSolution

   We compute the probability that three randomly chosen entries sum to an odd number, then the conditional probability of that event given they lie in a single row or column, and add them. The result simplifies to $\frac{17}{21}$, which is option (B).

   ---

   Concept & Intuition

   The matrix has 9 entries. We pick 3 of them uniformly at random.

   • For event A (odd sum), we need to count how many triples have an odd total. Since odd/even depends only on parity, we first classify the 9 numbers by parity: 1,3,5,7,9 are odd (5 odds); 2,4,6,8 are even (4 evens). The sum of three numbers is odd iff we have an odd number of odd entries among them — i.e., 1 or 3 odds.
   • For event B (all in one row or one column), we count triples that lie entirely in a single row (3 rows, each row has 3 entries → 1 triple per row) or entirely in a single column (3 columns, each column has 3 entries → 1 triple per column). That gives $3+3=6$ triples.
   • Then $P(A/B)$ is the fraction of those 6 triples that also have an odd sum.

   We compute both probabilities and add them.

   ---

   Step-by-step

   1. Total number of ways to choose 3 entries from 9

   $\binom{9}{3} = 84.$

   2. Count triples with odd sum (event A)
      • Case 1: exactly 1 odd, 2 evens Choose 1 odd from 5 odds: $\binom{5}{1}=5$ Choose 2 evens from 4 evens: $\binom{4}{2}=6$ Total: $5 \times 6 = 30$ triples.
      • Case 2: exactly 3 odds, 0 evens Choose 3 odds from 5 odds: $\binom{5}{3}=10$ Total: $10$ triples.
      • So $|A| = 30 + 10 = 40$. Hence

   $P(A) = \frac{40}{84} = \frac{10}{21}.$

   3. Count triples in a row or column (event B)
      • Rows: 3 rows, each row has exactly 1 triple (all three entries). So 3 triples.
      • Columns: 3 columns, each column has exactly 1 triple. So 3 triples.
      • Total: $|B| = 6$. Hence

   $P(B) = \frac{6}{84} = \frac{1}{14}.$

   4. Count triples that are both in a row/column AND have odd sum (event $A \cap B$)

      Check each row and column for odd sum:

      • Row 1: $\{1,2,3\}$ → sum = 6 (even) → not in A.
      • Row 2: $\{4,5,6\}$ → sum = 15 (odd) → in A.
      • Row 3: $\{7,8,9\}$ → sum = 24 (even) → not in A.
      • Column 1: $\{1,4,7\}$ → sum = 12 (even) → not in A.
      • Column 2: $\{2,5,8\}$ → sum = 15 (odd) → in A.
      • Column 3: $\{3,6,9\}$ → sum = 18 (even) → not in A. So exactly 2 triples (row 2 and column 2) satisfy both. Hence $|A \cap B| = 2$.

   5. Conditional probability $P(A/B)$

   $P(A/B) = \frac{|A \cap B|}{|B|} = \frac{2}{6} = \frac{1}{3}.$

   6. Add the two probabilities

   $P(A) + P(A/B) = \frac{10}{21} + \frac{1}{3} = \frac{10}{21} + \frac{7}{21} = \frac{17}{21}.$

   Tip

   A common mistake is to compute $P(A/B)$ using the full sample space instead of restricting to B. Always remember: conditional probability uses only the outcomes in B as the denominator.

   ✓Final answer

   The correct option is (B).

   ANSWER: B

6. TG EAPCET 2022Set eng-2022-07-19-FN1 markMCQ
   Q.If $A$ and $B$ are two events of a random experiment such that $P(\overline{A}) = \dfrac{2}{3}$, $P(B) = \dfrac{4}{15}$ and $P(A \cap \overline{B}) = \dfrac{1}{5}$, then $\sqrt{195 \left[ P\left(B \mid (A \cup \overline{B})\right) + P(A \cup B) \right]} =$ (A) 9 (B) 11 (C) 13 (D) 15

   ›Reveal solutionSolution

   This problem requires us to calculate probabilities of various event combinations (complement, intersection, union) and a conditional probability using fundamental set theory identities. We then substitute these values into the given expression to find the final numerical result. The final value is $\boxed{11}$.

   To solve this problem, we need to systematically break down the given expression and calculate each probability term using the fundamental rules of probability and set theory. The key is to correctly apply the formulas for complements, unions, intersections, and conditional probabilities, often using set identities to simplify complex event descriptions.

   Here's a step-by-step approach:

   1. Determine $P(A)$ from $P(\overline{A})$:

      The probability of an event $A$ and its complement $\overline{A}$ always sum to 1.

      $P(A) + P(\overline{A}) = 1$

      Given $P(\overline{A}) = \frac{2}{3}$, we can find $P(A)$:

      $P(A) = 1 - P(\overline{A}) = 1 - \frac{2}{3} = \frac{1}{3}$.

   2. Determine $P(A \cap B)$ using $P(A \cap \overline{B})$:

      The event $A$ can be partitioned into two mutually exclusive events: $A \cap B$ (A and B both occur) and $A \cap \overline{B}$ (A occurs, but B does not).

      $P(A) = P(A \cap B) + P(A \cap \overline{B})$

      We are given $P(A \cap \overline{B}) = \frac{1}{5}$ and we found $P(A) = \frac{1}{3}$.

      So, $P(A \cap B) = P(A) - P(A \cap \overline{B}) = \frac{1}{3} - \frac{1}{5}$.

      To subtract these fractions, we find a common denominator, which is 15:

      $P(A \cap B) = \frac{5}{15} - \frac{3}{15} = \frac{2}{15}$.

   3. Calculate $P(A \cup B)$:

      The probability of the union of two events $A$ and $B$ is given by the addition rule.

      $P(A \cup B) = P(A) + P(B) - P(A \cap B)$

      We have $P(A) = \frac{1}{3}$, $P(B) = \frac{4}{15}$ (given), and $P(A \cap B) = \frac{2}{15}$ (from Step 2).

      $P(A \cup B) = \frac{1}{3} + \frac{4}{15} - \frac{2}{15}$.

      Using a common denominator of 15:

      $P(A \cup B) = \frac{5}{15} + \frac{4}{15} - \frac{2}{15} = \frac{5+4-2}{15} = \frac{7}{15}$.

      This is the first part of the sum inside the square root.

   4. Prepare for $P(B \mid (A \cup \overline{B}))$: Identify the intersection term:

      The conditional probability $P(X \mid Y)$ is defined as $\frac{P(X \cap Y)}{P(Y)}$. Here, $X=B$ and $Y=(A \cup \overline{B})$.

      So, we need to find $P(B \cap (A \cup \overline{B}))$.

      Using the distributive property of set intersection over union:

      $B \cap (A \cup \overline{B}) = (B \cap A) \cup (B \cap \overline{B})$.

      The event $B \cap \overline{B}$ means that event $B$ occurs AND event $B$ does NOT occur, which is impossible. Thus, $B \cap \overline{B} = \emptyset$.

      So, $B \cap (A \cup \overline{B}) = (B \cap A) \cup \emptyset = B \cap A$.

      Therefore, $P(B \cap (A \cup \overline{B})) = P(A \cap B)$.

      From Step 2, we know $P(A \cap B) = \frac{2}{15}$. This is the numerator for our conditional probability.

   5. Prepare for $P(B \mid (A \cup \overline{B}))$: Calculate $P(\overline{B})$:

      Similar to Step 1, we use the complement rule for event $B$.

      $P(\overline{B}) = 1 - P(B)$.

      Given $P(B) = \frac{4}{15}$:

      $P(\overline{B}) = 1 - \frac{4}{15} = \frac{15-4}{15} = \frac{11}{15}$.

   6. Prepare for $P(B \mid (A \cup \overline{B}))$: Calculate $P(A \cup \overline{B})$:

      This is the denominator for our conditional probability. We use the addition rule for $A$ and $\overline{B}$.

      $P(A \cup \overline{B}) = P(A) + P(\overline{B}) - P(A \cap \overline{B})$

      We have $P(A) = \frac{1}{3}$ (from Step 1), $P(\overline{B}) = \frac{11}{15}$ (from Step 5), and $P(A \cap \overline{B}) = \frac{1}{5}$ (given).

      $P(A \cup \overline{B}) = \frac{1}{3} + \frac{11}{15} - \frac{1}{5}$.

      Using a common denominator of 15:

      $P(A \cup \overline{B}) = \frac{5}{15} + \frac{11}{15} - \frac{3}{15} = \frac{5+11-3}{15} = \frac{13}{15}$.

   7. Calculate $P(B \mid (A \cup \overline{B}))$:

      Now we have both the numerator and the denominator for the conditional probability.

      $P(X \mid Y) = \frac{P(X \cap Y)}{P(Y)}$

      $P(B \mid (A \cup \overline{B})) = \frac{P(B \cap (A \cup \overline{B}))}{P(A \cup \overline{B})} = \frac{P(A \cap B)}{P(A \cup \overline{B})}$.

      Substituting the values from Step 4 and Step 6:

      $P(B \mid (A \cup \overline{B})) = \frac{2/15}{13/15} = \frac{2}{13}$.

      This is the second part of the sum inside the square root.

   8. Calculate the sum inside the square root:

      We need to find $P\left(B \mid (A \cup \overline{B})\right) + P(A \cup B)$.

      From Step 7, $P\left(B \mid (A \cup \overline{B})\right) = \frac{2}{13}$.

      From Step 3, $P(A \cup B) = \frac{7}{15}$.

      Sum $= \frac{2}{13} + \frac{7}{15}$.

      To add these fractions, find a common denominator, which is $13 \times 15 = 195$.

      Sum $= \frac{2 \times 15}{13 \times 15} + \frac{7 \times 13}{15 \times 13} = \frac{30}{195} + \frac{91}{195} = \frac{30+91}{195} = \frac{121}{195}$.

   9. Calculate the final expression:

      The expression we need to evaluate is $\sqrt{195 \left[ P\left(B \mid (A \cup \overline{B})\right) + P(A \cup B) \right]}$.

      Substitute the sum we just calculated:

      $\sqrt{195 \times \frac{121}{195}}$.

      The $195$ in the numerator and denominator cancel out:

      $\sqrt{121}$.

      $\sqrt{121} = 11$.

   The final value is 11. Comparing this with the given options, it matches option (B).

   ✓Final answer

   The value of the expression is $\boxed{11}$.

7. TG EAPCET 2026Set eng-2026-05-10-FN1 markMCQ
   Q.Three persons A, B, C planned to have a running race among themselves. If the probability that A wins the race is thrice that of B and the probability that B wins the race is $\dfrac{3}{2}$ times that of C, then the difference in probabilities of A and C to win the race is (A) $\dfrac{2}{3}$ (B) $\dfrac{1}{2}$ (C) $\dfrac{5}{14}$ (D) $\dfrac{3}{7}$

   ›Reveal solutionSolution

   With $P(A)=\tfrac{9}{14},\ P(C)=\tfrac{2}{14}$, the difference is $P(A)-P(C)=\dfrac12$.

   Let $P(C)=p$. Then $P(B)=\dfrac{3}{2}p$ and $P(A)=3\,P(B)=\dfrac{9}{2}p$.

   The three probabilities sum to $1$ (one of them must win):

   $\frac{9}{2}p+\frac{3}{2}p+p=7p=1\ \Rightarrow\ p=\frac{1}{7}.$

   Hence

   $P(A)=\frac{9}{2}\cdot\frac17=\frac{9}{14},\qquad P(C)=\frac17=\frac{2}{14}.$

   The required difference is

   $P(A)-P(C)=\frac{9}{14}-\frac{2}{14}=\frac{7}{14}=\frac12.$

   ✓Final answer

   The difference in the winning probabilities of A and C is $\dfrac12$ — option (B).

8. TG EAPCET 2026Set eng-2026-05-09-AN1 markMCQ
   Q.In a Poisson distribution with parameter $\lambda$, if $5P(X=3) = P(X=5)$, then $P(X=2) =$ (A) $\dfrac{25}{e^5}$ (B) $\dfrac{50}{e^{10}}$ (C) $\dfrac{30}{e^6}$ (D) $\dfrac{40}{e^8}$

   ›Reveal solutionSolution

   The key idea is to use the Poisson probability formula $P(X=k) = \frac{e^{-\lambda} \lambda^k}{k!}$ and the given relation $5P(X=3) = P(X=5)$ to solve for $\lambda$, then compute $P(X=2)$. The final answer is $\frac{50}{e^{10}}$, which corresponds to option (B).

   The Poisson distribution models the number of events in a fixed interval when events occur independently at a constant average rate $\lambda$. The probability mass function is $P(X=k) = \frac{e^{-\lambda} \lambda^k}{k!}$ for $k = 0, 1, 2, \dots$. Here, the condition $5P(X=3) = P(X=5)$ gives a direct equation in $\lambda$ because the $e^{-\lambda}$ factor cancels, leaving a simple algebraic relation. Once $\lambda$ is found, plugging into $P(X=2)$ yields the answer.

   1. Write the given condition using the Poisson formula:

   $5 \cdot \frac{e^{-\lambda} \lambda^3}{3!} = \frac{e^{-\lambda} \lambda^5}{5!}$

   The factor $e^{-\lambda}$ cancels on both sides (since $\lambda$ is finite), giving:

   $5 \cdot \frac{\lambda^3}{6} = \frac{\lambda^5}{120}$

   2. Simplify the equation. Multiply both sides by 120 to clear denominators:

   $5 \cdot \frac{\lambda^3}{6} \cdot 120 = \lambda^5$

   Compute $120/6 = 20$, so $5 \cdot 20 \cdot \lambda^3 = \lambda^5$, i.e., $100 \lambda^3 = \lambda^5$.

   3. Assuming $\lambda > 0$ (since it's a rate parameter), divide both sides by $\lambda^3$:

   $100 = \lambda^2$

   Hence $\lambda = 10$ (we take the positive root because $\lambda$ is a mean, always positive).

   Watch out

   A common mistake is to forget that $\lambda$ must be positive. Also, do not cancel $\lambda^3$ if $\lambda = 0$ — but $\lambda = 0$ would make all probabilities zero, which contradicts the given relation (since $P(X=3)$ and $P(X=5)$ would both be zero, making $5 \cdot 0 = 0$ trivially true, but that degenerate case is not intended in such problems). Always check that the solution makes physical sense.

   4. Now compute $P(X=2)$ with $\lambda = 10$:

   $P(X=2) = \frac{e^{-10} \cdot 10^2}{2!} = \frac{e^{-10} \cdot 100}{2} = 50 e^{-10}$

   5. Write $e^{-10}$ as $\frac{1}{e^{10}}$, so:

   $P(X=2) = \frac{50}{e^{10}}$

   Tip

   Notice that the answer choices are all of the form $\frac{\text{integer}}{e^{\text{integer}}}$. Once you find $\lambda = 10$, the denominator $e^{10}$ immediately points to option (B). This can be a quick sanity check.

   ✓Final answer

   The value is $\boxed{\frac{50}{e^{10}}}$, which corresponds to option (B).

9. TG EAPCET 2024Set eng-2024-05-09-FN1 markMCQ
   Q.If the probability that a student selected at random from a particular college is good at mathematics is 0.6, then the probability of having two students who are good at mathematics in a group of 8 students of that college standing in front of the college is (A) $\dfrac{2^6 \times 3^2 \times 7}{5^8}$ (B) $\dfrac{2^6 \times 3^2 \times 7}{5^6}$ (C) $\dfrac{2^8 \times 3^2 \times 7}{5^6}$ (D) $\dfrac{2^8 \times 3^2 \times 7}{5^8}$

   ›Reveal solutionSolution

   This is a binomial trial with $n=8$, $p=0.6$. $P(X=2)=\binom{8}{2}(0.6)^2(0.4)^6 = \dfrac{2^{8}\times 3^{2}\times 7}{5^{8}}$, option (D).

   Binomial model

   Each student is independently good at mathematics with probability $p = 0.6 = \dfrac{3}{5}$, so $q = 0.4 = \dfrac{2}{5}$. For $n=8$ students, the number good at mathematics is binomial, and we want exactly two:

   $P(X=2) = \binom{8}{2}\,p^{2}\,q^{6} = \binom{8}{2}\left(\frac{3}{5}\right)^{2}\left(\frac{2}{5}\right)^{6}.$

   Simplify

   $\binom{8}{2}=28,\qquad \left(\frac{3}{5}\right)^{2}=\frac{3^{2}}{5^{2}},\qquad \left(\frac{2}{5}\right)^{6}=\frac{2^{6}}{5^{6}}.$

   $P(X=2) = 28\cdot\frac{3^{2}}{5^{2}}\cdot\frac{2^{6}}{5^{6}} = \frac{28\cdot 3^{2}\cdot 2^{6}}{5^{8}}.$

   Write $28 = 2^{2}\times 7$:

   $= \frac{2^{2}\times 7\times 3^{2}\times 2^{6}}{5^{8}} = \frac{2^{8}\times 3^{2}\times 7}{5^{8}}.$

   ✓Final answer

   $P(\text{exactly two}) = \dfrac{2^{8}\times 3^{2}\times 7}{5^{8}}$. The correct option is (D).

   ANSWER: D

10. TG EAPCET 2021Set eng-2021-08-04-FN1 markMCQ
    Q.If $\dfrac{^{22}P_{r+1} : ^{20}P_{r+2}}{ } = 11 : 52$ then $r =$ (A) 3 (B) 5 (C) 7 (D) 9

    ›Reveal solutionSolution

    This problem involves simplifying a ratio of permutations using the permutation formula and then solving the resulting algebraic equation. We find that $r=7$.

    Concept and Intuition

    Permutations deal with the arrangement of distinct items. The number of permutations of $r$ items chosen from $n$ distinct items is denoted by $^nP_r$ and calculated using the formula:

    $^nP_r = \frac{n!}{(n-r)!}$

    For this formula to be valid, certain conditions must be met:

    1. $n$ must be a non-negative integer.
    2. $r$ must be a non-negative integer.
    3. $n \ge r$. This ensures that the term $(n-r)!$ is well-defined (i.e., we do not have a factorial of a negative number).

    In this problem, we are given a ratio of two permutation expressions. The key to solving such problems is to:

    1. Apply the permutation formula to expand each term.
    2. Simplify the resulting factorial expressions by cancelling common terms. Remember that $k! = k \times (k-1)!$ and generally $k! = k \times (k-1) \times \dots \times (k-m+1) \times (k-m)!$. This property is crucial for simplifying ratios of factorials.
    3. Solve the algebraic equation for $r$.
    4. Finally, check if the obtained value of $r$ satisfies the conditions for permutations for both terms in the original problem.

    Let's apply these ideas to the given problem.

    Step-by-step Solution

    1. Write down the given ratio and apply the permutation formula.

       We are given the ratio $\dfrac{^{22}P_{r+1}}{^{20}P_{r+2}} = \dfrac{11}{52}$.

       Using the formula $^nP_r = \frac{n!}{(n-r)!}$:

       • For $^{22}P_{r+1}$: $n=22$, $r_{perm} = r+1$. So, $^{22}P_{r+1} = \frac{22!}{(22-(r+1))!} = \frac{22!}{(21-r)!}$.
       • For $^{20}P_{r+2}$: $n=20$, $r_{perm} = r+2$. So, $^{20}P_{r+2} = \frac{20!}{(20-(r+2))!} = \frac{20!}{(18-r)!}$.

       Substituting these into the ratio:

    $\frac{\frac{22!}{(21-r)!}}{\frac{20!}{(18-r)!}} = \frac{11}{52}$

    2. Simplify the expression by rearranging and expanding factorials. We can rewrite the left side by inverting the denominator and multiplying:

    $\frac{22!}{(21-r)!} \times \frac{(18-r)!}{20!} = \frac{11}{52}$

    Now, we expand the larger factorials in terms of smaller ones to facilitate cancellation:
    *   $22! = 22 \times 21 \times 20!$
    *   $(21-r)! = (21-r) \times (20-r) \times (19-r) \times (18-r)!$
    
    Substitute these expansions into the equation:
    

    $\frac{22 \times 21 \times 20!}{(21-r)(20-r)(19-r)(18-r)!} \times \frac{(18-r)!}{20!} = \frac{11}{52}$

    3. Cancel common factorial terms. Notice that $20!$ in the numerator and denominator cancel out. Similarly, $(18-r)!$ in the numerator and denominator cancel out:

    $\frac{22 \times 21}{(21-r)(20-r)(19-r)} = \frac{11}{52}$

    Calculate the product in the numerator: $22 \times 21 = 462$.
    

    $\frac{462}{(21-r)(20-r)(19-r)} = \frac{11}{52}$

    4. Solve the algebraic equation for $r$. Cross-multiply to eliminate the denominators:

    $462 \times 52 = 11 \times (21-r)(20-r)(19-r)$

    Divide both sides by $11$:
    

    $\frac{462 \times 52}{11} = (21-r)(20-r)(19-r)$

    $42 \times 52 = (21-r)(20-r)(19-r)$

    $2184 = (21-r)(20-r)(19-r)$

    Let $x = 20-r$. Then $21-r = x+1$ and $19-r = x-1$.
    The equation becomes:
    

    $2184 = (x+1)x(x-1)$

    $2184 = x(x^2-1)$

    $2184 = x^3 - x$

    We need to find an integer $x$ that satisfies this equation. We can test integer values:
    *   If $x=10$, $10^3 - 10 = 1000 - 10 = 990$ (too small).
    *   If $x=12$, $12^3 - 12 = 1728 - 12 = 1716$ (too small).
    *   If $x=13$, $13^3 - 13 = 2197 - 13 = 2184$ (This is correct!).
    So, $x=13$.
    
    Now substitute back $x = 20-r$:
    

    $13 = 20-r$

    $r = 20-13$

    $r = 7$

    5. Verify the value of $r$ against permutation conditions. For $r=7$:
       • For $^{22}P_{r+1} = ^{22}P_{7+1} = ^{22}P_8$: Here $n=22$, $r_{perm}=8$. Since $22 \ge 8 \ge 0$, this is valid.
       • For $^{20}P_{r+2} = ^{20}P_{7+2} = ^{20}P_9$: Here $n=20$, $r_{perm}=9$. Since $20 \ge 9 \ge 0$, this is valid. Both conditions are satisfied, so $r=7$ is the correct solution.

    ✓Final answer

    The value of $r$ is $\boxed{7}$.

11. TG EAPCET 2025Set eng-2025-05-02-AN1 markMCQ
    Q.A typist claims that he prepares a typed page with typo errors of 1 per 10 pages. In a typing assignment of 40 pages, if the probability that the typo errors are at most 2 is $p$, then $e^{2}p=$ (A) $5$ (B) $13$ (C) $13e^{-2}$ (D) $5e^{-2}$

    ›Reveal solutionSolution

    The problem models rare typos with a Poisson distribution (mean = 4 typos in 40 pages). The probability of at most 2 typos is $p = e^{-4}(1 + 4 + 8) = 13e^{-4}$, so $e^{2}p = 13e^{-2}$, matching option (C).

    We have a typist who averages 1 typo per 10 pages. That’s a small rate for a rare event over a fixed “area” (pages). When events are rare and independent, the Poisson distribution is the natural choice — it counts the number of occurrences in a fixed interval when the average rate is known. Here, the “interval” is 40 pages.

    Why Poisson?

    • Each page has a small chance of a typo.
    • Pages are independent.
    • We care about the count of typos, not their arrangement. The Poisson distribution with parameter $\lambda$ (the mean number of events in the interval) fits perfectly.

    ---

    1. Find the average number of typos in 40 pages. The rate is 1 typo per 10 pages, so in 40 pages:

    $\lambda = \frac{1 \text{ typo}}{10 \text{ pages}} \times 40 \text{ pages} = 4.$

    2. Set up the Poisson probability formula. For a Poisson random variable $X$ with mean $\lambda$:

    $P(X = k) = \frac{e^{-\lambda} \lambda^k}{k!}.$

    We need $P(X \leq 2) = P(X=0) + P(X=1) + P(X=2)$.

    3. Compute each term.

       • $P(X=0) = \frac{e^{-4} \cdot 4^0}{0!} = e^{-4}$.
       • $P(X=1) = \frac{e^{-4} \cdot 4^1}{1!} = 4e^{-4}$.
       • $P(X=2) = \frac{e^{-4} \cdot 4^2}{2!} = \frac{16e^{-4}}{2} = 8e^{-4}$.

    4. Sum them to get $p$.

    $p = e^{-4} + 4e^{-4} + 8e^{-4} = 13e^{-4}.$

    5. Compute $e^{2}p$.

    $e^{2}p = e^{2} \cdot 13e^{-4} = 13e^{-2}.$

    Watch out

    A common mistake is to use the binomial distribution with $n=40$ and $p=0.1$ (since 1/10 = 0.1). That would give a different (and incorrect) answer because the Poisson is the exact limit for rare events over a continuous “exposure” — and here the problem’s phrasing (“1 per 10 pages”) strongly signals a rate, not a per-page probability.

    Tip

    Notice that $e^{2}p$ simplifies to $13e^{-2}$, which is already one of the options. No need to approximate numerically — the algebra gives the answer directly.

    ✓Final answer

    The correct option is (C).

    ANSWER: C

12. TG EAPCET 2023Set eng-2023-05-13-AN1 markMCQ
    Q.If $X$ is a Poisson variate satisfying the condition $3P(x=2) = P(x=4)$ then $P(x=6) =$ (A) $\dfrac{162}{5e^6}$ (B) $\dfrac{108}{5e^6}$ (C) $\dfrac{324}{5e^6}$ (D) $\dfrac{648}{5e^6}$

    ›Reveal solutionSolution

    The key idea is to use the Poisson probability mass function $P(X=k) = \frac{e^{-\lambda} \lambda^k}{k!}$, set up the given condition $3P(X=2) = P(X=4)$, solve for $\lambda$, then compute $P(X=6)$ and match it to one of the options. The final result is $\frac{324}{5e^6}$, which corresponds to option (C).

    We start with the Poisson distribution. A Poisson random variable $X$ with mean $\lambda$ has probability mass function

    $P(X = k) = \frac{e^{-\lambda} \lambda^k}{k!}, \quad k = 0, 1, 2, \dots$

    The problem gives a relationship between $P(X=2)$ and $P(X=4)$. This lets us solve for $\lambda$, the only unknown parameter. Once we know $\lambda$, we can compute $P(X=6)$ directly.

    ---

    1. Write the given condition in terms of $\lambda$. We have $3P(X=2) = P(X=4)$. Substituting the Poisson formula:

    $3 \cdot \frac{e^{-\lambda} \lambda^2}{2!} = \frac{e^{-\lambda} \lambda^4}{4!}$

    2. Cancel the common factor $e^{-\lambda}$ (since $e^{-\lambda} > 0$ for any finite $\lambda$). This gives:

    $3 \cdot \frac{\lambda^2}{2} = \frac{\lambda^4}{24}$

    3. Simplify both sides. Left: $3 \cdot \frac{\lambda^2}{2} = \frac{3\lambda^2}{2}$. Right: $\frac{\lambda^4}{24}$. So:

    $\frac{3\lambda^2}{2} = \frac{\lambda^4}{24}$

    4. Solve for $\lambda$. Multiply both sides by 24:

    $24 \cdot \frac{3\lambda^2}{2} = \lambda^4 \quad \Rightarrow \quad 36\lambda^2 = \lambda^4$

    Rearranging:

    $\lambda^4 - 36\lambda^2 = 0 \quad \Rightarrow \quad \lambda^2(\lambda^2 - 36) = 0$

    Since $\lambda > 0$ for a Poisson distribution (mean cannot be zero if we have nonzero probabilities for $k=2,4$), we take $\lambda^2 = 36$, so $\lambda = 6$.

    Tip

    A common mistake is to forget that $\lambda$ must be positive. The solution $\lambda = 0$ would make all probabilities zero except $P(X=0)=1$, which doesn't satisfy the given equation meaningfully.

    5. Now compute $P(X=6)$ with $\lambda = 6$.

    $P(X=6) = \frac{e^{-6} \cdot 6^6}{6!}$

    6. Simplify $6^6$ and $6!$. $6^6 = 46656$ (or keep as $6^6$). $6! = 720$. So:

    $P(X=6) = \frac{e^{-6} \cdot 46656}{720}$

    7. Reduce the fraction. Divide numerator and denominator by 144 (since $46656 \div 144 = 324$ and $720 \div 144 = 5$):

    $P(X=6) = \frac{324}{5} \cdot e^{-6} = \frac{324}{5e^6}$

    Watch out

    Watch out: $e^{-6}$ is often written as $1/e^6$, so the answer is $\frac{324}{5e^6}$, not $\frac{324}{5}e^6$ or something similar.

    8. Match with the options. The expression $\frac{324}{5e^6}$ corresponds exactly to option (C).

    ✓Final answer

    The correct option is (C).

    ANSWER: C