If the probability of rain on any given day in City X is 50%, what is probability that it rains on exactly 4 days in a 5 day period? Answers:
A) 2/5
B) 4/5
C) 3/16
D) 4/32
E) 5/32
One possible way is rain-rain-rain-rain-no rain.   The probability of this is 1/2*1/2*1/2*1/2*1/2 = 1/32   The number of possible ways is 5C4 = 5, so we multiply this by 5.   P(rain on exactly 4 days) = 5*1/32 = 5/32   The answer is 5/32.
<result>E</result>
If the probability of rain on any given day in City X is 50%, what is probability that it rains on exactly 4 days in a 5 day period?