Bunuel
If x and y are positive integers and if x is a prime factor of y, is x^2 a factor of y?
(1) x < 6
(2) y = 36
ANSWER: B
This question is a test of knowledge of primes.
1: x could be any of 1,2,3,4,5. but we dont know that what y actually is. y could be more than x OR same as x since any number is a factor of itself. if x=y then x^2 is defnitely NOT a factor of y. if x<y then it almost defnitely is a factor of y. BUT we can't tell. so 1 is NOT SUFFICIENT
2: this is straight to the point. 36 has only 2 and 3 as prime factors. the square of either gives you a value that is still a factor of 36. So we can definitely say YES 2 is SUFFICIENT
NB: you may restructure the question stem in your head as "Is Y a prime number?" such that once you see any of 1 or 2 that shows Y is NOT a prime or is a prime, you could QUICKLY tell it's sufficient. 1 did not talk about Y at all. 2 shows quickly that Y is not a prime. eureka!