求助一道prep数学题

On Jane's card account, the average daily balance for a 30-day billing cycle is the average (arithmetic mean) of the daily balances at the end of each the 30 days. At the beginning of a certain 30-day billing cycle, Jane's card account had a balance of $600. Jane made a payment of $300 on the account during billing cycle. If no other amounts were added for subtracted from the account during the billing cycle, what wah 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

answer: D

这题没看懂，各位帮忙讲一下。谢谢~

自己顶~~~

能不能帮忙讲一下？thank you~

顶!!

題目的意思就是要求 30天的平均數

第一天有600, 中間有提出過300, 沒有存過錢

多谢chianalin!!

昨天主要是被这句话搞糊涂了:

"On Jane's card account, the average daily balance for a 30-day billing cycle is the average (arithmetic mean) of the daily balances at the end of each the 30 days":

 现在也没太明白....

谢谢，看了以前的讨论，可是还不是很明白

hitlzc说

“题的意思是：一个30天帐期的平均日余额是：30天每天结束时的余额的平均数。

所以在付款300前，每天余额都是600，之后每天余额都是300，知道哪天付款即可。”

可是At the beginning of a certain 30-day billing cycle, Jane's card account had a balance of $600. Jane made a payment of $300 on the account during billing cycle. 的意思真的是这样吗？

开始的时候余额是600，那个300的payment怎么看出之前之后的呢？不是during billing cycle，难道不是during整个billing cycle吗？

我英语不太好，大家见笑啦，不过实在是不明白呀~

大家指教~

Thank you,sammy生米!

祝1次高分过G!!!

昨天有点晕，今天重新开了一下题目，突然发现昨天问了一个弱弱的问题

已经明白了，谢谢各位~