If the probability of rain on any given day in City X is 20%, what is probability that it rains on exactly 3 days in a 4 day period? Choose the correct choice
A) 16/625 B) 8/125 C) 6/125 D) 4/25 E) 3/25
One possible way is rain-rain-rain-no rain.   The probability of this is 1/5*1/5*1/5*4/5 = 4/625   The number of possible ways is 4C3 = 4, so we multiply this by 4.   P(rain on exactly 3 days) = 4*4/625 =16/625   The answer is 16/625.
<result>A</result>
If the probability of rain on any given day in City X is 20%, what is probability that it rains on exactly 3 days in a 4 day period?