Math CentralQuandaries & Queries


Question from seulki, a student:

coin tossed 30 times, what is the probability that the heads show up fewer than 17 times?

Hi Seulki,

This is a binomial distribution problem. There is an experiment, tossing a coin, which is repeated 30 times and the probability of tossing a head is 1/2 on each of the 30 trials. Thus for example the probability that the head shows up more than 12 times is

binomial probability

I am not sure how you are to evaluate this. You can find each one of the terms and add them, you can use a binomial table or you can use the normal approximation to the binomial.


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