Is positive integer x a prime number? 1) [m]x^2+x[/m] ≤ 1

[GMATinsight]

Is positive integer x a prime number?

1) x^2+x ≤ 10
2) x does not have odd number of factors

Source: www.GMATinsight.com

Answer: option C

[Sionainn@PrincetonReview]

This is a great one for plugging in.

Start with statement 1. The only positive numbers that satisfy this statement are 1 and 2. 1 is not prime and 2 is prime. So this statement is not sufficient. Narrow the choices to B, C and E.

Now statement 2. x can be 2 since it's factors are 1 and 2, so it has an even number of factors. But x can also be 6 since its factors are 1, 2, 3 and 6. 2 is prime, but 6 is not prime. So this statement is also not sufficient. Narrow the choices to C and E.

Now combine both statements. The only value that satisfies both statements is 2. So together both statements are sufficient and the answer is C.

Take care,
Sionainn