求助-一道prep数学题

fionaoyangf

on Jane's credit account, the average daily balance for a 30-day billing cycle is the average of the daily balabces at the end of the each of the 30-day. at the beginning of the certain 30-day lilling cycle, Jane's credit card account had a balance of $600.Jane made a payment of $300 on the account during the cycle. if no other amounts were added to or subtracted from the account during the billing cycle. what was the average daily balance on Jane's account for the billing cycle?

(1) Jane's payment was credited on the 21st day of the billing cycle.
(2)the average daily balance through the 25th day of the billing cycle was $540.

答案是D，我连题目都没看懂、。。。求助牛人解答一下，谢谢。

fionaoyangf

谢谢，已经找到了，而且以后再有什么问题不用都来这里问了。。。

切尔西

这个题目确实蛮绕的，你可以去看下PREP详解版，那里的那个解释我认为很清楚的，希望对你有帮助