A fair coin is tossed 3 times. Find the probability of obtaining exactly 2 heads.

Correct Answer: Option B

Explanation

Let the probability of getting a head = p = (frac{1}{2}) and that of tail = q = (frac{1}{2})

((p + q)^{3} = p^{3} + 3p^{2}q + 3pq^{2} + q^{3})

In the equation above, (p^{3}) and (q^{3}) are the probabilities of 3 heads and 3 tails respectively 

 while, (p^{2}q) and (pq^{2}) are the probabilities of 2 heads and one tail and 2 tails and one head respectively.

Probability of exactly 2 heads = (3p^{2}q = 3(frac{1}{2})^{2}(frac{1}{2}))

= (frac{3}{8})