Question

A coin is tossed 7 times. Find the probablility of getting exactly 4 heads.

Answer 1

how many possible ways are there to toss 7 coins? how many of them end up with exactly 7 heads?

Answer 2

there are 2*2*2*2*2*2*2 = 2^7 different cointoss possibilities.

(7 choose 4) of them = (7!)/(4!*(7-4)!) of them result in exactly 4 heads.

Answer 3

all 128 outcomes are equally likely, and 35 of them result in 4H3T, so the answer is 35/128.