How to Cancel Variables in GMAT Data Sufficiency

Hi GMATters,

We’re all taught that “you need at least as many equations as you have variables.” In fact, that’s one of the first principles in a lot of GMAT texts.

The simple fact that it’s in the damn GMAT books is almost undoubtedly why tricky DS questions love to punk you by having a variable simply disappear as part of the structure of the question.

In short, when you reorganize the information given at the beginning of the question (and occasionally when you plug a Statement in–but not in this video), you’ll find that what you thought was a variably really just falls out.

Why was there a variable there in the first place if it wasn’t necessary?

Look, this is like a three-year-old asking “where the sun sets.” It begs a longer, philosophical discussion of a “placeholder variable,” but mercifully I won’t bother you with the details.

After all, this is GMAT-land, and getting the job done is more important than the dreaded “whys.”

Enjoy!

Rowan

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PPS I mean if you really do care to hear about placeholder variables, let me know and I’ll explain further. I’m geeky like that.