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GabrielL588
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Foundations of GMAT Math, pg 49, Q14!

by GabrielL588 Mon Aug 29, 2016 2:41 pm

Hi all, I have a very simple and lame question.

On the Foundations of GMAT Math book, Drill 2, #14, on page 49..
Question 14.... - 5 ^ 2, I answered 25 because a negative number squared is positive. The answer key says the answer is - 25 (negative 25), and the explanation is as follows...
-5 ^ 2
- (5 ^ 2 ) = - 25

Thoughts? Why would you ignore the fact that there is a negative sign in front of the 5 until after the exponent? I know in PEMDAS you do exponent first, but if this is the case how do you tell the difference between a negative number and just a number with a minus sign in front of it, especially when this isn't an equation but instead is just asking me to "Evaluate the expression"?

Thanks!

Gabe
RonPurewal
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Re: Foundations of GMAT Math, pg 49, Q14!

by RonPurewal Fri Sep 02, 2016 7:20 pm

the "–" sign, in front, constitutes multiplication by –1.
exponents come before multiplication.
done.

__

in terms of algebra, you probably know that "–x^2" means –(x^2), and not (–x)^2.
...and numbers follow the same rules that variables follow.