求助OG DS161题

julia_juer

不是很明白这道题的意思。。。希望有高手可以指导一下！！！！万分感谢！！！！
161.Beginning in January of last year, Carl made deposits of $120 into his account on the 15th of each month for several cinsecutive months and then made withdrawls 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

julia_juer

太感谢了！！！！

ReneeKuang

非高手解答。
这题的1和2合起来，可推出Carl是从六月份开始取钱的。因为条件1说，在四月底他帐户上有少于$2625的钱。条件2说，在六月底他帐户上有少于$2675的钱。题目里已知他从一月开始，每月存$120，到五月时帐上有$2600。如果他继续在六月存$120的话，那六月底就会有$2720。但条件2说，在六月底他帐上的钱少于$2675。所以可以推出他是从六月开始每月取$50的。知道了这一点，就可推算出他全年帐上的余额情况，从而求出range。