求教一道数学题，实在没明白为什么？

yin0883

2. A parking garage rents parking spaces for $10 per week or $30 per month. How much does a person save in a year by renting by the month rather than by the week?
(A) $140
(B) $160
(C) $220
(D) $240
(E) $260
答案为什么选B啊？苦思不得解

owenwei

a year =52 week or 12 month

by week: 52*10=520

by month:30*12=360

difference = 160

sysxy1987

晕，问的是月租比每星期租便宜多少。

10*365/7 - 30*12

yin0883

...奥 原来一年52周阿。。。 傻了