标题: 请问一道数学题 [打印本页] 作者: Rosemarry102 时间: 2010-1-6 22:10 标题: 请问一道数学题 90. 8266-!-item-!-187;#058&005947 On Jane's credit 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 of the 30 days. At the beginning of a certain 30-day billing cycle, Jane's credit card account had a balance of $600. Jane made a payment of $300 on the account during the billing 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.作者: a10285 时间: 2010-1-6 22:44
题意是问一个月账户余额的平均值？ （1）可得出前20天$600,后10天$300, 可得答案~ （2）设 在前25天中的第n+1天付费的，则600*n+300*（25-n）=540*25 算得n=5，即在6th天的payment，至此和（1）同，得出答案~