og12 date sufficiency 问题求助

斯坦福桥的车夫 · 发表于 2011-1-17 16:51:14

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 withdraws of $50 from the account on the 15th of each remaining months of last year.If the closing balance of Carl's account for May of last year was $2600,what was the range of the monthly closing balance of Carl's account last year?(1) Last year the closing balance of Carl's account for April was less than $2625.
(2) Last year the closing balance of Carl's account for June was less than $2675.
跪谢各位高人了，最好帮我把题目也翻译了

sdcar2010 · 发表于 2011-1-17 22:59:22

There are 12 month in a year.

Starting from January, Carl made deposite of $120 every month for the first N months.

Then for the rest of 12-N month, Cart withdrew $50 every month

Do you know the range of the closing balance of Carl's account last year if in May his ballance was $2600?

Theoretically, only 12 possible choices depending on the value of N.

1) If in April the balance was less than $2625, then in May Carl deposited money. Otherwise, 2600+50 =2650 would be the closing balance in April.
2) If in June the balance was less than 2675, then in June Carl withdrew money. Otherwise, 2600 + 120 = 1720 would be the closing balance in June.

So if you combining 1) and 2), you can know for sure that N = 5, sufficient.

og12 date sufficiency 问题求助

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