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OG 13 #180 explanation

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OG 13 #180 explanation

by jeph86 » Wed Feb 17, 2016 4:21 pm
if m^-1=-1/3, then m^-2 is equal to?

a) -9
B) -3
C) -1/9
D) 1/9
D) 9

I don't understand how the answer is D. my choice was E. Can someone explain this answer?

thanks
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by Brent@GMATPrepNow » Wed Feb 17, 2016 4:33 pm
jeph86 wrote:if m^-1=-1/3, then m^-2 is equal to?

a) -9
B) -3
C) -1/9
D) 1/9
D) 9
Here's one approach:
m^-1 = -1/3
So, (m^-1)² = (-1/3)²
Simplify to get: m^-2 = (-1/3)(-1/3)
So, m^-2 = 1/9
Answer: D

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by Brent@GMATPrepNow » Wed Feb 17, 2016 4:35 pm
jeph86 wrote:if m^-1=-1/3, then m^-2 is equal to?

a) -9
B) -3
C) -1/9
D) 1/9
D) 9
Another approach:
If m^-1 = -1/3, then m = -3
Notice that (-3 )^-1 = -1/3

So, m^-2 = (-3)^-2
= 1/(3^2)
= 1/9
Answer: D

For more info on negative exponents, we our free video: https://www.gmatprepnow.com/module/gmat ... video/1028

Cheers,
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by jeph86 » Wed Feb 17, 2016 4:54 pm
thanks Brent,

the second approach makes more sense to me. appreciate your quick response
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