请教大家两道OG12上的题..

mereimoun

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


此题选D
我银行方面知识欠缺..完全不懂这题啥意思...


What is the greatest common divisor of positive integers m and n ?
（1）m is a prime number.
(2) 2n = 7m
此题选C

mereimoun

非常感谢....

xiaoyuexing

第一道题。

说一个什么破循环有30天。然后有个叫简的人丫卡的额度是600，手痒刷了300 。

题目问在这么一个破循环里，简丫的平均额度是多少。

条件1：简丫从第21天才开始手痒刷卡。
条件2：平均额度在25天内一直是540 。

条件1可知，简丫的额度在前20天内一直是600，21天开始，手痒刷卡刷了300，额度变成600-300，因此平均额度就是（600*20+300*10）/30

条件2可知，简丫前25天额度一直是540，所以鸭肯定在这1-25天内刷过了，否则这个额度应该是600才对。所以最后的5天简丫的额度只有300了。因此平均额度就是
（540*25+300*5）/30

综上，本题选D 。

mereimoun

谢谢^_^

yoyo9012

抱歉第一题没有看懂题目意思。请教其他NN了。
第二题，我的做法是：1，2，肯定首先排除独立成立可能。
考虑C，M，N是正整数（没有0了）。7是ODD乘以M 要等于一个偶数（2N 肯定都是偶数）。M又是

质数，这样质数中只有2是偶数。所以此题得到M=2，N=7。有了具体数字就能得到最大公约数了。