og12 DS161求解~

木南子 · 发表于 2012-4-6 15:51:29

161. Beginning in January of last year, Carl made deposits
of $120 into his account on the 15th of each month
for several consecutive months and then made
withdrawals of $50 from the account on the 15th of
each of the remaining months of last year. There were
no other transactions in the account last year. If the
closing balance of Carl’s account for May of last year
was $2,600, what was the range of the monthly
closing balances of Carl’s account last year?
(1) Last year the closing balance of Carl’s account
for April was less than $2,625.
(2) Last year the closing balance of Carl’s account
for June was less than $2,675.

没看懂什么意思....

provensky · 发表于 2012-4-6 16:21:28

题目中表示每个月只有两种可能，1，存进120，2，取出50。已知5月的余额为2600。
（1）四月的余额小于2625，如果五月取出50的话，四月的余额为2650，大于2625所以不成立。那只可能是五月存进120，这样得出四月的余额为2480。符合条件。于是就知道了五月是存钱的，但是由于不知道什么时候开始取钱，所以算不出最后答案。（1）不充分。
（2）思考方法同（1）已知六月余额小于2675，五月余额2600。可以得出六月是取出50后余额为2550。但是不知道是从几月份开始取钱的，所以算不出答案。（2）不充分。
（1）＋（2）充分，因为已经知道五月是存钱，以及从六月之后一直是取钱。这样就能算出哪个月余额最多，哪个月最少。从而求出题目要求的RANGE。具体不用计算，节省时间。
答案选C

Tazuya · 发表于 2012-4-6 17:47:03

嗯。看了一会懂了。谢谢。
不然我连题目都读不透

og12 DS161求解~

所属分类: GMAT考试

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