Bunuel wrote:
If x and y are positive integers, what is the value of y?
(1) y − x = 3
(2) x and y are prime numbers
Target question: What is the value of y? Statement 1: y − x = 3 Clearly NOT SUFFICIENT
Statement 2: x and y are prime numbersClearly NOT SUFFICIENT
Statements 1 and 2 combined The GMAT loves to test us on the fact that, although there are infinitely many prime numbers, ONLY ONE of those primes is EVEN
That is, 2 is the only EVEN prime number. All other primes are ODD.
Statement 2 tells us that x and y are prime.
And statement 1 tells us that y − x = 3
Hmmm, y - x = 3, which is odd.
This means that one value is EVEN, and the other value is ODD (since this is the only way to get an odd difference)
If one number is EVEN, then that number must be 2.
So, if y - x = 3, it must be the case that y = 5 and x = 2
So, the answer to the target question is
y = 5Since we can answer the
target question with certainty, the combined statements are SUFFICIENT
Answer: C
Cheers,
Brent
_________________
Test confidently with gmatprepnow.com
close
79% (01:16) correct 
