GMAT蓝皮书数学第二题,是不是答案错了啊.Aparkinggaragerentsparkingspacesfor$10perweekor$30permonth.Howmuchdoesapersonsaveinayearbyrentingbythemonthratherthanbytheweek?(A)$140(B)$160(C)$220(D)$240(E)$

Question

GMAT蓝皮书 数学第二题,是不是答案错了啊.
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
my solution is as following:
the rent in a year by the month:30*12=$260
the rent in a year by the week:10*4*12=$480
hence the person save $480-$360=$120
but the answer is B（given from the net) or C (given from the key printed on the books)
please tell me why I am wrong?is the wrong answer?
Thanks a lot

Answer 1

一年365天,365/7约等于52,一年也就是520刀.
按月算,一年是30*12=360刀.
因此省下的钱就是520-360=160刀.
选B.
在题目没有说明一个月按四个星期算的时候,则需要自己算出一年星期数的准确数字.