请教三道PREP模考题的解题思路，谢谢！

debralee · 发表于 2008-8-3 09:30:00

都是PREP模考的题，不明白，请哪位NN给提供一下思路？谢谢。

If n is a positive integer and r is the remainder when (n+1)(n-1) is divided by 24, what's the valude of r?

(1) 2 is not a factor of n; (2) 3 is not a factor of n. (C)

if 2/5 of the students at college of C are business majors, what is the number fo female students at College C? (C)

(1) 2/5 of the male students at colege C are business majors

(2) 200 of the female students at college of C are business majors

If x is an integer, is median of the 5 numbers shown greater than the average of the 5 numbers? (E)

(1) x>6

(2)x is greater than the median of the 5 numbers

jh1904 · 发表于 2008-8-3 09:55:00

1。条件1，n为奇数，n-1, n+1 为相邻两偶数，乘积必为2^3=8的倍数 (2*4, 4*6, 6*8, ...), 无法确定除24的余数。

条件2，n不为3的倍数，n+1, n-1必有1为3的倍数，无法确定除24的余数。

1+2，(n+1)(n-1) 同时为8与3的倍数，除24，余数为0。

2. 2/5 of the students major in business

(1) 2/5 of the male students major in business, so 2/5 of the female students major in business.

(2) 200 of the female students major in business, 200 is 2/5 of all female students. There are 500 female students.

Statement 1 and 2 together are sufficient

3. You need to provide the 5 numbers in the stem.

sarahzhensh · 发表于 2008-8-3 10:12:00

楼上好强阿！以前我是用另一种方法做的第一题，虽然做出来了。但是很麻烦。今天知道简单方法了,关键在"相邻两个偶数乘积是8的倍数"

Thank you!

debralee · 发表于 2008-8-3 15:28:00

谢谢热心人！

所属分类: GMAT考试