Source: Revised GRE PDF 1st Ed. Section 6: Math; #5 (p. 84)


The average (arithmetic mean) of 100 measurements is

The average (arithmetic mean) of 100 measurements is 23, and the average of 50 additional measurements is 27. Quantity A : The average of the 150 measurements Quantity B : 25 Quantity A is greater., Quantity B is greater., The two quantities are equal., The relationship cannot be determined from the information given.

2 Explanations


Alan Romero

[(23*100)+(27*50)] / 150 = 24.33

Nov 16, 2012 • Comment

Chris Lele, Magoosh Tutor

Hi Alan,
You want to be careful not to actually do the math on QC, unless you are uncertain of the intuitive approach. Doing the math takes time and can yield an incorrect answer.
Following the intuition that the average is going to "lean" towards 23, and therefore has to be less than 25 gets you the answer really quickly :).

Dec 14, 2012 • Reply

Kalina Gajda

Hi Chris! Is the equation that Alan did correct?

Apr 15, 2019 • Reply

Adam Lyons, Magoosh Tutor

Yes, the math is correct, but it is much better to use the intuitive approach here.

Apr 17, 2019 • Reply


Gravatar Chris Lele, Magoosh Tutor

Sep 26, 2012 • Comment

Add Your Explanation

You must have a Magoosh account in order to leave an explanation.

Learn More About Magoosh