GATE | GATE 2017 MOCK II | Question 38

In a random experiment, suppose 3 unbiased coins are tossed simultaneously, what is the probability of getting at least 2 Heads ?
(A) 1/2
(B) 3/4
(C) 7/8
(D) 1/8


Answer: (A)

Explanation: Since, the coins are unbiased
P(H) = P(T)=1/2
Required = > P(At least 2 Heads)
=> 1-P(No heads)-P(Exactly one head)
=> 1-P(TTT)-P(HTT | THT | TTH)
=> 1-(1/8)-3*(1/8)
=> 1-4*(1/8)
=> 1/2

Answer :- A


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