[問題]GMAT prep 2- 28

[superruby]

28.If M is a positive odd interger between 2 and 30, then M is divisible by how many different positive preime numbers?
1. m is not divisible by 3
2. m is not divisible by 5
Answer-A

I choose c, odd number except multiple of 3 are
5,7,11,13,15.....
number of prime factor 1,1, 1, 1, 2,
-> 1.not sufficient
So choice A is not the right answer?

天呀! 做GMAT prep模考錯10題, 做GWD都沒這麼慘,是不是題目特別難呀?

[clbb]

15是3的倍數....

[superruby]

恍然大悟~謝謝指點
天啦!我後天要考了還這麼白目....

[GMAT]

為啥條件(2)不行?m is not divisible by 5->3,7,9,11,13,17,19，不也都是1嗎?

[clbb]

(2)的話21有2個質因數