Fool Me Once GMAT Questions

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October 22, 2021

Here’s a popular Fool Me Once question/riddle:

If a plane crashes directly on the border of Canada and the United States, in which country should you bury the survivors?

The answer is neither, since it’s not cool to bury survivors. If you’ve already heard that riddle, then you automatically knew the answer. If today is the first time you encountered the riddle, then you’ll undoubtedly know the answer next time you hear it. That’s what makes this a Fool Me Once question.

Fool Me Once (FMO) questions are questions that leave a larger-than-average mental footprint in the part of your mind that houses your mistakes, and the very existence of those footprints significantly reduces the likelihood you’ll repeat the same mistake. There are several GMAT questions that can fall in this category. For example:

If x is a non-zero integer, what is the value of x?

(1) x^4x = x¹⁶

(2) (x^x)(x²) = x⁶

Many students will automatically conclude that, since each equation features equal bases, we can equate the exponents to find that x = 4 is the only solution to each equation, in which case the answer is D.

Not so.

While x = 4 is one solution to x^4x = x¹⁶ (the equation in statement 1), the values x = 1 and x = -1 also satisfy the equation, which means statement 1 is not sufficient (here’s my full solution).

Similarly, the equation (x^x)(x²) = x⁶ has 2 solutions: x = 1 and x = 4, which means statement 2 is not sufficient.

Even when we combine the two equations, we can only conclude that x equals either 1 or 4, which means the statements combined aren’t sufficient, which means the answer is E.

As you can imagine, it's useful to see as many FMO question before your test. So, here are some more to practice with:

Fool Me Once GMAT Questions

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