A coin is tossed for fixed number of times. If the probability of

Question

A coin is tossed for fixed number of times. If the probability of getting 6 heads is equal to the probability of getting 9 heads, then the probability of getting 3 heads is

A. 455/2^15
B. 89/2^16
C. 89/2^15
D. 99/2^15
E. 267/2^16

(adapted from gmatfree)

ankitgoswami · Answer

Since the probability of getting 6 heads is equal to the probability of getting 9 heads, therefore the coin was tossed 9+6 = 15 times

So Probability of getting 3 heads in 15 tosses = \frac{15!}{(3! 12!)} * \frac{1}{2^{15} }

Solving it we get  \frac{455}{2^{15} }

Ans is  A

Foreheadson · Answer

X!/(6!*(X-6)! = X!/(9!*(X-9)!)

the only way this is possible is when X=9+6=15.

So 3C15 = 455.

divide by 2^15 to account for 15 tosses. Answer choice A.

A coin is tossed for fixed number of times. If the probability of

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