求助一DS题~！~

云小熙 · 发表于 2011-7-3 23:33:19

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 begining of 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 accounts were added to or substracted from the account during the billing cycle, what was the average daily balance on Jane's account for the billing cycle?

a) Jane's payment was credited on the 21st day of the billing cycle.
b)The average daily balance theough the 25th day of the billing cycle was $540.

麻烦大虾们帮忙分析分析~~~万谢！

云小熙 · 发表于 2011-7-4 07:16:04

自己来顶下！up~up~up~~~~~~麻烦各位NN帮忙解答一下啦~~~~~~~~~~~~~

gaohongmin · 发表于 2011-7-4 07:57:31

我认为应该选D
1)总共的周期是30天，只要知道是哪天取出的$300就可以选出这个平均数
2）知道了前25天的平均数是540，而后五天的平均数肯定是300，加权平均就好了

ALGT · 发表于 2011-7-4 12:24:57

设第x天花了300，则n天之后的日平均y：

y ＝ (600（x-1）+300(n-x+1))/n

a）x＝21
b）当n＝25时，y＝540

云小熙 · 发表于 2011-7-4 13:08:37

懂了！非常感谢~~~

gx911 · 发表于 2011-7-4 14:14:52

同意2楼D，不需要算具体值

求助一DS题~！~

所属分类: GMAT考试

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