If the probability of rain on any given day in Chicago during the summer is 50%, independent of what happens on any other day, what is the probability of having exactly 3 rainy days from July 4 through July 7, inclusive? Choose the correct choice from the following answers:
A) 1 / 4
B) 1 / 8
C) 3 / 8
D) 3 / 16
E) 5 / 16

Rationale: one case is rainy - rainy - rainy - not rainy . the probability of this case is ( 1 / 2 ) ^ 4 = 1 / 16 the number of possible cases is 4 c 3 = 4 . p ( exactly 3 rainy days ) = 4 * 1 / 16 = 1 / 4 the answer is a .
Answer: A