求助几道GMATPrep数学题

nightsky

1
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.
答案：C

我没有申请过信用卡（穷人），这道题我压根没看明白什么意思～～～

2
If the drama club and music club are combined, what percent of the combined membership will be male?

(1)  Of the 16 members of the drama club, 15 are male.
(2)  Of the 20 members of the music club, 10 are male.
答案 E

为什么选E，而不是C呢？那个16和20不是说的各个俱乐部的全部成员吗？？

3
Alice's take-home pay last year was the same each month, and she saved the same fraction of her take-home pay each month.  The total amount of money that she had saved at the end of the year was 3 times the amount of that portion of her monthly take-home pay that she did not save.  If all the money that she saved last year was from her take-home pay, what fraction of her take-home pay did she save each month?

答案：1/5

没看明白什么意思～～～～

[此贴子已经被作者于2008-8-12 9:44:57编辑过]

杰西卡的戈多

第一题看到题干就退却了……

2.没有说同时参加两个club的人数 所以E

3.一年存下来的钱是每月没存部分的3倍

设一个月的take-home pay是A,每月存的比例是n

则nA*12=3（1-n）A

所以n=1/5

nightsky

感谢“杰西卡的戈多”！

第3题我明白了。

第2题，说合并不是说两个俱乐部成员都加在一起吗？其实有些时候，我感觉经常会遇到一些很模糊的条件。原本我都以为GMAT出题比较简单，所以不愿把问题想得特别复杂………………

看来第1题的确有点讨厌，我们考老外的时候一定要用古文！！

杰西卡的戈多

第二题是数学集合的问题，题目没有给出两个club合并后的交集部分

第一题翻prep看了看，上面写得答案是D

From (1), we know that Jane’s daily balances at the end of the first 20 days of the billing  cycle were $600.  From the 21st day to the 30th day of the cycle, the daily balances were all 300.  From this, we can calculate the average daily balance for the 30-day billing cycle.

From (2), we know that the payment was made some time between the 1st and 25th day; other-
wise, the average would have been $600.  (We can actually calculate that it was made on the 21st day, but it is irrelevant.)  Hence the daily balance at the end of the 26th to the 30th
day must be 300.  From this, we can calculate the average for the 30-day cycle:

（25*540 + 5*300）/30=500

Thus the correct answer is D.

杰西卡的戈多

呼~翻译了一下~

对于一个30天的结算周期来说，平均日结余是一个30天后每日结余的算术平均值。在30天的结算周期开始时，jane的信用卡余额是600，jane在这个结算周期里付款300.如果在这个周期里没有其他钱款从这个帐户存入或扣除，这个周期jane帐户的平均日结余是多少？

（1）jane是在第21天还款的
（2）前25天的平均日结余是540

解释：
（1）前20天的平均日结余是600，21st-30th的平均日结余是300。所以一个月的是（20*600 + 10*300）/30=500

（2）因为前25天的平均日结余<600，所以那300是前25天中的某天打入的，所以后5天的平均日结余都是300。所以一个月的是 （25*540 + 5*300）/30=500

所以各自都充分

batmanhm

请问楼主是在prep模考中做数学，还是prep破解的数学？哪里有下载破解的数学部分啊？

谢谢了

nightsky

感谢“杰西卡的戈多”，第一题我也明白了。答案的确是D，是我写错了^_^

另外，楼上的“batmanhm”需要破解的，我发一个附件，东西是从CHASEDREAM里面下的。

 

[此贴子已经被作者于2008-8-13 9:11:02编辑过]