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The Quest for 700: Weekly GMAT Challenge (Answer)

Yesterday, Integrated Learning posted a 700 level GMAT question on our blog. Today, they have followed up with the answer:

Ans. C

To be a perfect square, you must be able to take the square root of Q.  Practically, that means both x and y need to be even numbers.

Statement 1: We learn that Q has at least 4 3’s and 2 7’s in its prime factors, but we don’t know there aren’t more than that.  Q could have 5 3’s, which case y would be 5 and you would not be able to square root Q.

Statement 2: Since 243 is 35 and 343 is 73, Q has less than 5 3’s, and less than 3 7’s in its prime factors.  But again, y could be any number less than 5 and x any number less than 3, even or odd.

Together – Q has exactly 4 3’s and 2 7’s in its prime factors and is therefore a square of an integer.

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