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If m^(-1) = -1/3 (OG16)

This topic has 3 expert replies and 0 member replies

Forum: If m^(-1) = -1/3 (OG16)

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C

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If m^(-1) = -1/3, then m^(-2) is equal to

A) -9
B) -3
C) -1/9
D) 1/9
E) 9

OA: D

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GMAT/MBA Expert

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boomgoesthegmat wrote:
If m^(-1) = -1/3, then m^(-2) is equal to

A) -9
B) -3
C) -1/9
D) 1/9
E) 9

OA: D
m^(-1) = 1/m

We're told that m^(-1) = -1/3
This means that 1/m = -1/3
So, we know that m = -3

This means that m^(-2) = (-3)^(-2)
= 1/9
= D

RELATED RESOURCE (video):
Negative exponents: https://www.gmatprepnow.com/module/gmat-powers-and-roots/video/1028

Cheers,
Brent

_________________
Brent Hanneson – Creator of GMATPrepNow.com
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GMAT/MBA Expert

Post
boomgoesthegmat wrote:
If m^(-1) = -1/3, then m^(-2) is equal to

A) -9
B) -3
C) -1/9
D) 1/9
E) 9

OA: D
Another solution:
Given: m^(-1) = -1/3
Square both sides to get: [m^(-1)]^2 = (-1/3)^2
Simplify: m^(-2) = (-1/3)(-1/3)
So, m^(-2) = 1/9

Answer: D

RELATED RESOURCE (video)
- Laws of exponents - part I: https://www.gmatprepnow.com/module/gmat-powers-and-roots/video/1025

Cheers,
Brent

_________________
Brent Hanneson – Creator of GMATPrepNow.com
Use our video course along with Beat The GMAT's free 60-Day Study Guide

Sign up for our free Question of the Day emails
And check out all of our free resources

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GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months!
Post
boomgoesthegmat wrote:
If m^(-1) = -1/3, then m^(-2) is equal to

A) -9
B) -3
C) -1/9
D) 1/9
E) 9
Notice that m^(-2) = [m^(-1)]^2, therefore,

m^(-2) = (-1/3)^2 = 1/9

Alternate Solution:

We re-express m^(-1) as 1/m. We are given that m^(-1) = -1/3, so we see that m = -3.

To evaluate m^(-2), we substitute -3 for m, yielding (-3)^(-2) = 1/(-3)^2 = 1/9.

Answer: D

_________________
Jeffrey Miller Head of GMAT Instruction

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