求解两道PREP数学>_<

summer0103 · 发表于 2012-1-30 21:09:32

1.If n is a positive integer and r is the remainder when 4+7n is divided by 3,r=?
(1)n+1 is divisible by 3
(2)n＞20
答案A。

是不是指r=0？

2.The sum of positive integers x and y is 77.xy=?
(1)x=y+1
(2)x and y have the same tens digit
答案D

条件一好理解，条件二，xy有相同十位数，x、y可以有很多组合啊，34、33,35、32，怎么确定乘积呢。。我的思维就到这里了= =。

刘宣宣90117 · 发表于 2012-2-9 12:24:51

32+35 is not equal to 77

There are only 2 numbers that add up to 77 and have the same 10 digits. They are 38 and 39. Therefore either statement is sufficient - D
哈哈这个题很吭爹的~

stayinjuly · 发表于 2012-2-9 14:20:12

因为n+1被3整除,所以设n+1=3k,4+7n=4+7(3k-1)=21k-3,能被3整除,所以r=0

求解两道PREP数学>_<

所属分类: GMAT考试

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