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EXERCISE 8.1 · Q4

Q.Five cards are drawn successively with replacement from a well-shuffled deck of 52 cards. Find the probability that

(i) all the five cards are spades
(ii) only 3 cards are spades
(iii) none is a spade.
Maharashtra MsbshseTextbookSubjectiveImportance★★★★★
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Five cards are drawn WITH replacement, so each draw is an independent Bernoulli trial with p=1352=14p=\dfrac{13}{52}=\dfrac14 (spade) and q=34q=\dfrac34 (not spade); X∼B(5,14)X\sim B\left(5,\tfrac14\right).

  1. All five spades: P(X=5)=(14)5=11024P(X=5)=\left(\dfrac14\right)^5=\dfrac{1}{1024}.
  2. Only 3 spades: P(X=3)=5C3(14)3(34)2=10×164×916=901024=45512P(X=3)={}^{5}C_3\left(\dfrac14\right)^3\left(\dfrac34\right)^2=10\times\dfrac1{64}\times\dfrac9{16}=\dfrac{90}{1024}=\dfrac{45}{512}. …

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