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by ddm » Mon Sep 08, 2008 1:27 pm
A student first reduced a certain number by 20% and then increased it again by 20%. If the difference between the last number and the original number was 8, then the original number was:

(A) 200

(B) 250

(C) 300

(D) 450

(E) 400
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by VP_Jim » Mon Sep 08, 2008 3:50 pm
I think the easiest approach to this one is to simply test the answer choices. All you have to do is take each answer choice, decrease it by 20%, then increase that number by 20%, and see which one differs by 8 from the original answer choice.

For example...

Start with 200. Decrease it by 20% to 160. Then increase 160 by 20% to 192. Okay, we found the answer already, since 192 is 8 less than 200.

Note that, say, 400 won't work. 400 decreased by 20% is 320, then increase that by 20% to 384. 400 and 384 don't differ by 8, so 400 isn't the right answer.

Hope this helps!
Jim S. | GMAT Instructor | Veritas Prep
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