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BK87
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FDP Guide Pg. 37 #7

by BK87 Wed Nov 26, 2014 8:34 pm

Question:

Simplify: 8(3)(x)^2(3) over 6x

The solution according to the guide is 12x. My question is, why is the answer not 12x^2 over x? No where in the problem does it say that x does not equal zero. How come we are allowed to cancel out the x in the dominator?

Thanks.
tim
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Re: FDP Guide Pg. 37 #7

by tim Sat Nov 29, 2014 2:53 am

Any time you see a variable in the denominator, that is an implicit guarantee that the variable cannot be 0. Remember, you cannot divide by 0, so if you see the GMAT dividing by a variable, it is not 0.
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RonPurewal
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Re: FDP Guide Pg. 37 #7

by RonPurewal Sat Dec 06, 2014 12:50 pm

at the beginning of every official GMAT (and in the introduction to the math chapters in the OG), you'll see this specification: "All numbers are real numbers."

ordinarily, there will also be prohibitions that prevent this sort of thing from happening anyway. (e.g., if a denominator is x(x – 1), then the problem will specify that x ≠ 0 and x ≠ 1.) but, even if those prohibitions are absent, "all numbers are real numbers" still guarantees that you won't divide by zero.