Asked by nick
A coin is tossed 7 times. What is the probability of getting four heads. My teacher said that there is a formula involved but i don't know which one. How do i set it up?
Answers
Answered by
economyst
With a fair coin the probability of a given 7-flip series is equal to ANY 7-flip series. That is, P(HHHHTTT) = P(TTTHHHH) = P(THTHTHT)....
There are 2^7 = 128 possible 7-filp series. This is the denominator.
There are 4-choose-7 ways to have a 4 heads in 7 filps. 4-choose-7 is 7!/(4!*(7-4)!) = 35.
So, the probability is 35/128
There are 2^7 = 128 possible 7-filp series. This is the denominator.
There are 4-choose-7 ways to have a 4 heads in 7 filps. 4-choose-7 is 7!/(4!*(7-4)!) = 35.
So, the probability is 35/128
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