Multiples of 5?

[kprasadreddy]

Here is the question that I mentioned about

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

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

a) Statement 1 by itself is sufficient but statement 2 by itself is not
b) Statement 2 by itself is sufficient but statement 1 by itself is not
c) statements 1 and 2 taken together are sufficient
d) either statement by itself is sufficient
e) statements 1 and 2 together are not sufficient

Here is the explanation

1) Insufficient x < 15 could be 2,3,5,7,11,13 Eliminated A and D
2) Insufficient X-2 is a multiple of 5 Multiple of 5 are 0,5,10,15 and so on.2 more than 0 is 2 a prime number 2 more than 5 is 7 a prime number Answer is E

[ksb]

Good question. The key is to remember that '0' is a multiple of '5'.

Thanks for posting the question

[Anshu]

Shouldnt we consider negative values too? nowhere it is mentioned that X is a positive number.. so in that case if we consider x-2 as a multiple of five and put x-2 = -5 => x = -3. Please comment whether we should consider negative values for such questions or not.

Thanks

[ksb]

X is a prime number is mentioned in the question.

Prime numbers are a subset of natural numbers (positive integers). Therefore, we need not consider negative numbers.