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## The monthly sales (in thousands of $) at a certain... tagged by: swerve This topic has 1 expert reply and 0 member replies ### Top Member swerve Master | Next Rank: 500 Posts Joined 29 Oct 2017 Posted: 339 messages Followed by: 4 members #### The monthly sales (in thousands of$) at a certain...

Sun Nov 05, 2017 7:20 am
The monthly sales (in thousands of \$) at a certain restaurant for the past two years are given in the chart below:

Last year: 9, 9.5, 10, 10, 11, 11, 11, 11, 11, 12.5, 13, 13.
This year: 9, X, 10, 10, 11, 11, 11, 11, 11, Y, 13, 13.

If the standard deviation of the monthly sales is greater this year than last year, which of the following are possible values for X and Y?

A) 9 and 12.5
B) 10 and 11
C) 10 and 12.5
D) 11 and 11
E) 11 and 12.5

The OA is A.

Please, can any expert explain this PS question for me? I have many difficulties to understand why that is the correct answer. Thanks.

### GMAT/MBA Expert

Rich.C@EMPOWERgmat.com Elite Legendary Member
Joined
23 Jun 2013
Posted:
9445 messages
Followed by:
480 members
2867
GMAT Score:
800
Sun Nov 05, 2017 12:17 pm
Hi swerve,

Standard Deviation questions on the GMAT are never about calculating an actual Standard Deviation - they're about the CONCEPT behind SD (how "spread out" a group of numbers is). It's a relatively rare concept on Test Day - you'll probably see it just once.

In this question, we're given lots of data that we're essentially going to ignore. We're told to make this year's SD larger than last years, which means that we have to make this year's group of numbers "more spread out" than last year's group of numbers. Put simply, we're looking to replace X and Y with 2 numbers that are as "far apart" from one another as possible.

GMAT assassins aren't born, they're made,
Rich

_________________
Contact Rich at Rich.C@empowergmat.com

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