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The monthly sales (in thousands of $) at a certain...

This topic has 1 expert reply and 0 member replies

The monthly sales (in thousands of $) at a certain...

Post Sun Nov 05, 2017 7:20 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    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.

    Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!
    Post 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.

    The answer pair with the largest spread is

    Final Answer: A

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

    _________________
    Contact Rich at Rich.C@empowergmat.com

    Thanked by: swerve

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