求解- preceton revew math

cathyyan

cathyyan

图片打不开，只能key了，如下：

there is a 90% chance that a registed voters in Burghtown voted in last election. if 5 of registed votes are chosen at random, what's the approximate likehood exactly four of them voted in the last election.

a. 26.2%
b.32.8%
c. 43.7&
d.59.0%
e. 65.6%

answer: b

anistonlucky

0.9^4*0.1*5=0.328

cathyyan

请问大侠，0.9^4*0.1我明白，可为什么还要×5啊？

rwchinak

因为没有vote的那个人有5种情况