Problem Solving

This problem is an example from the Delta Course, but they do not give an answer. Please give it a try, and let me know if your answer matches mine. Thanks!

On any day in April in a certain city, the probability of rain is 50%. What is the probability of that it rains exactly 5 days during a 7 day period in April?

I did the following:

2^7 = 128, so 128 possible outcomes

7!/(5!2!) = 21

Answer = 21/128.

yes its correct
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