@mbajack's post

in GMAT Data Sufficiency Discussions
Updated 2 days ago

The average (arithmetic mean) N numbers is M. When the number x is removed, the average decreases by 3. What is the value of x? 

1) M + 3N = 21

2) N = 2M

Answer is here -

http://www.gmatprepnow.com/module/gmat-statistics/video/819 

I thought you need 2 equations with 2 unknowns

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mbajack
@mbajack  ·  0 karma

Don't you need 2 equations??

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WiziusCareers
@WiziusCareers  ·  0 karma

Hi

For any question on averages, it is a good idea to apply the formula as many times as the word "mean" appears in the question.

From the question:

Sum/N = M    => Sum = MN

When x is removed, the sum of numbers will be Sum - x.

(Sum - x)/(N - 1) = M - 3


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