[求助]一道概率题

gmataren

If the probability of rain on any given day in city X is 50%, what is the probability that it rains on exactly 3 days in a 5-day period?

tomrchu

同意～

mandyuuqq

 =C53(1/2)^3(1/2)^2

丁香花儿

做出来了，是C(5,3)*(.5)3*(1-.5)2=5/16