ISRO | ISRO CS 2011 | Question 61

Three coins are tossed simultaneously. The probability that they will fall two heads and one tail is
(A) 5/8
(B) 1/8
(C) 2/3
(D) 3/8

Answer: (D)
Explanation: Using Binomial Distribution, probability of 2 head and 1 tail:

nCk (p)k. (1-p)n-k

Here, n = 3, k = 2, prob(head) = p = 1/2, prob(tail) = (1-p) = 1/2

= 3C2 (1/2)2. (1/2)1
= 3 * (1/2)3
= 3/8 

Option (D) is correct.

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