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Four fair coins are tossed once. Calculate the probabilit...

Four fair coins are tossed once. Calculate the probability of having equal heads and tails.

A.

14

B.

38

C.

12

D.

1516

Correct answer is B

Let p(head)=p=12 and p(tail)=q=12

(p+q)4=p4+4p3q+6p2q2+4pq3+q4

The probability of equal heads and tails = 6p2q2=6(122)(122)

= 616=38.