Answer to GMAT Practice Question No 1

The following is the answer and explanation to GMAT Practice Question #1:

Answer: C

Explanation:
Right away with this question, recognize that it’s a remainder problem. As with all questions, knowing the topic significantly narrows the number of ways you can approach the problem. This is a good thing – there are only a few ways to look at remainder questions. In order of effectiveness, we suggest: first, plug in numbers. If that doesn’t work, apply your conceptual understanding of remainders. If that, too, proves to not be helpful, then resort to algebra.

Before going into the statements, figure out what the answer could be. A number, x is divided by 18, that means the remainder can be any number between 0 and 17, inclusive. If we can figure out what it is exactly, we have enough information, if not, we don’t.

The first statement tells us that the remainder is 7 when x is divided by 9. Let’s plug in numbers. x could be 7, 16, 25, 34, 43…. Then try each of these with 18. You will quickly see that for 7, 25, and 43 the remainder is 7, but for 16 and 34, the remainder is 16. Since we have two answers, this isn’t enough information.

The second statement just tells us that x is even. That could be any even number, so that’s not enough information.

Looking at them together, notice that from statement one we learn that when x is odd, the remainder is 7, but when x is even, the remainder is 16. Since we know from statement two that x is definitely even, we know the remainder must be 16. So we have enough from the two statements combined.

The answer and explanation to GMAT Practice Question #1 was written by Integrated Learning, a company that provides professional and private one on one tutoring services.