If X is a prime number, what's the value of X? (1) X

Question

If X is a prime number, what's the value of X?

(1) X < 15
(2) (X-2) is a multiple of 5.

The correct answer is E....why?

I think it's C and here's how I solved it

from (1), X can be 2,3,5,7,11 and 13
from (2) X is 7 because 7 - 2 = 5 which is a multiple of 5

gmatprep09 · Answer

The answer can be E here:

1 is not sufficient.
2 is not sufficient either.

Together take values of X as 2, then 2-2 = 0 , which is a multiple of 5 (as 0*5=0). (0 is a multiple of 5).
X=7 will also give a multiple of 5.

Thus E.

Jozu · Answer

Hi,

It is because there can be many values of x that fulfills the second statement.

For example:
17-2 = 15, multiple of 5 too.

We do not know whether X is 15 or 5, hence insufficient.

humans · Answer

You are right I got to the same conclusion. What is the source of this question and OE. Or may be they are not considering 5 as multiple of 5.

gmatprep09 · Answer

X cannot be 17 because X<15. Hence the values possible for X are 2 and 7 (prime nos) where X-2 is a multiple of 5.

humans · Answer

Not sure but seems the only plausible explanation. Thanks

MontrealGirl · Answer

but from (1), we know that the prime number should be less than 15

MontrealGirl · Answer

Kaplan practice test

yezz · Answer

If X is a prime number, what's the value of X?

(1) X < 15
(2) (X-2) is a multiple of 5.

obviously each alone is not suff

both

x-2 = 5a

x = 5a-2.. x = 3 or13,23.....etc

from one
x<15 ie x = 2or3,5,7,11,13

the intersection of the 2 one and two is 3,13 we cant determine one single value...thus E

GMAT TIGER · Answer

A small correction note for a typo: x = 5a + 2.. x = 2 or 7 or 12 or 17 or so on....

icandy · Answer

Leaving out zero is the reason why we will get C.

If X is a prime number, what's the value of X? (1) X < 15