PrepGMAT 2007

goo_puu3 · 发表于 2007-6-22 16:50:00

For every positive even integer n, h(n)= product of even integer from 2 to n, inclusive. P is the smallest prime factor. P is

A. between 2 and 10

B. between 10 and 20

C. between 20 and 30

D. between 30 and 40

E. greater than 40

Answer is E.

Please help. How to get this answer...

mypiao · 发表于 2007-6-22 16:57:00

题目没写完把,这题精华里面有,记得是求h(100)+1的P
个人思路如下:
h(100)=2*4..........................*100=2^50(1*2*3*4..............*50)
可知h(100)最大的质数因子是47.
而h(100)+1跟h(100)肯定互质,那h(100)+1最小的质因子肯定不包含从1到50的质数,最小也要大于47,那就是E了

sammy生米 · 发表于 2007-6-22 20:55:00

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goo_puu3 · 发表于 2007-6-23 00:54:00

mypiao, 你很聪明吗. 一看就知道, 我问得是这道题. 谢谢了. - BY

PrepGMAT 2007

PrepGMAT 2007

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