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GMAT Math Strategy to make hard questions easier

As you know, our approach at Dominate the GMAT is to train you to out-think the GMAT test makers and get more right answers at all costs! When you’re faced with a difficult GMAT problem solving question, one of our coolest, most powerful GMAT math strategies is called:


WIBNI is an acronym that stands for “wouldn’t it be nice if.” The premise of this strategy is to solve an easier version of a hard question to discover a general rule that allows you to solve the original, more difficult version.

WIBNI is actually a mindset that you should adopt on the GMAT in general, a habit of thinking when you’re faced with a difficult, complicated, ugly math problem, rather than just capitulating and resigning yourself to a wrong answer. This mindset should train you to search your repertoire of other non-standard math techniques to apply to question types that are good candidates. And it’s also a strategy that will help you to “think through” difficult GMAT problem solving questions like this:

K = 25 x 29 x 31 x 37 x 41

Question: A decrease of 1 in which of the factors above would result in the greatest decrease in K?

(A) 25
(B) 29
(C) 31
(D) 37
(E) 41

Obviously, the test makers don’t want you do actually calculate out that entire product (which would be 34,094,575, by the way!). So what to do?

Hopefully you have the intuition to realize that the answer must be either choice (A) or choice (E), the extreme factor values; a few students might suspect choice (C), since it’s the median factor, but that would be incorrect.

So, the question you should be asking yourself is, “What exactly is it that I don’t like about this problem that I could use WIBNI to change?” Obviously, it’s the huge product. It’s difficult to work with, and thus hard to figure out whether you should reduce the smallest factor or the largest factor to effect the greatest decrease in K.

So what would be an easier version of this more difficult problem?

Well…Wouldn’t It Be Nice If the problem were instead:

K = 2 x 3 x 4

Question: A decrease of 1 in which of the factors above would result in the greatest decrease in K?

(A) 2
(B) 3
(C) 4

See how much easier this version of the problem is? We can actually do this math and prove to ourselves what the right answer is.

The original value of K in this easier version is 2 x 3 x 4 = 24. If you subtract 1 from the smallest factor, 2, you now get a new product of 12 (a difference of 12). If you subtract 1 from the largest factor, 4, you get a new product of 18 (a difference of 6). If you subtract 1 from the median factor, 3, you get a new product of 16 (a decrease of 8).

Clearly, from this WIBNI strategy, decreasing the smallest factor by 1 yields the greatest overall decrease in the original value of K. This reveals a general mathematical principle that will apply to any version of this same question setup, including our original, more difficult question. The answer to that question is therefore (A) as well.

With a little practice, you can train your eye to quickly identify when to use this killer WIBNI GMAT math strategy and therefore get more difficult GMAT math questions correct — in other words, to dominate the GMAT!