Write a program to find average of three numbers.

Exercises · Q17

Q. Write a program to find average of three numbers.

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Concept understanding — Simple Interest Calculation

Simple Interest: The Cost of Borrowing (or the Reward for Saving)

Imagine you lend a friend ₹100. A year later, they return the ₹100. You're even — but you also missed the chance to use that ₹100 yourself for a whole year. That inconvenience has a price. In finance, that price is called interest.

Simple interest is the most straightforward way to calculate that price. It says: the interest you earn (or pay) each year is a fixed percentage of the original amount you started with — no matter how many years pass.

The Core Intuition

Think of it like renting money. If you rent a car for a day, you pay a fixed daily rate. If you rent it for 5 days, you pay 5 times that daily rate. Simple interest works the same way:

The Principal (P) is the amount you lend or borrow — the "car."
The Rate (R) is the daily rental charge, expressed as a percentage of the car's value — the "rent per day."
The Time (T) is how many days you keep the car — the number of years.

The total rent (interest) is just: daily rent × number of days.

The Precise Statement

\text{Simple Interest (SI)} = \frac{P \times R \times T}{100}

Where:

P = Principal (the original sum of money)
R = Rate of interest per year (in percent)
T = Time period (in years)

The Total Amount (A) you get back (or owe) at the end is:

A = P + \text{SI}

Why Divide by 100?

The rate $R$ is given as a percentage — say 10%. "10% per year" means you get ₹10 for every ₹100 you lend, each year. So for a principal $P$ , the interest for one year is:

\frac{10}{100} \times P = 0.10 \times P

That's the same as $\frac{P \times R}{100}$ . For $T$ years, you multiply by $T$ , giving $\frac{P \times R \times T}{100}$ .

A Worked Example

You deposit ₹2000 in a bank that offers 8% simple interest per year. You leave it for 3 years.

P = ₹2000
R = 8
T = 3

\text{SI} = \frac{2000 \times 8 \times 3}{100} = \frac{48000}{100} = ₹480

So after 3 years, you earn ₹480 in interest. Your total amount becomes:

A = 2000 + 480 = ₹2480

Tip

Notice that each year you earn exactly the same interest: $\frac{2000 \times 8}{100} = ₹160$ . Year 1: ₹160, Year 2: another ₹160, Year 3: another ₹160. The interest never grows because it's always calculated on the original ₹2000, not on the growing balance.

The Key Property (and its Limitation)

Simple interest is linear — the interest grows at a constant rate each year. This makes it easy to calculate and understand. …

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Read the three numbers, add them, divide by 3:

a = float(input("Enter first number: "))
b = float(input("Enter second number: "))
c = float(input("Enter third number: "))
average = (a + b + c) / 3
print("Average =", average)

Sample run (10, 20, 30):

Enter first number: 10
Enter second number: 20
Enter third number: 30
Average = 20.0
``` …

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Sum the three inputs and divide by 3 — average = (a + b + c) / 3 — remembering the parentheses; inputs 10, 20, 30 give 20.0.

The concept is again operator precedence in a formula: division binds tighter than addition, so the sum must be parenthesised before dividing by 3.

# Average of three numbers
a = float(input("Enter first number: "))
b = float(input("Enter second number: "))
c = float(input("Enter third number: "))

average = (a + b + c) / 3
print("Average =", average)

Key lines:

float() lets the program average decimal values (e.g. marks like 78.5) — int() would reject them.
(a + b + c) / 3 — with the parentheses the sum is computed first; / then returns a float, so the average is exact even when the sum isn't divisible by 3.

Sample run:

Enter first number: 10
Enter second number: 20
Enter third number: 30
Average = 20.0
``` …

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Q.Write a program to find average of three numbers.

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