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by Max@Math Revolution » Tue May 26, 2020 1:24 am

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[GMAT math practice question]

The figure shows a square with a side length of 5m. A side of the square is divided equally into 5 segments. The square is cut into 5 pieces, as the figure shows. What is the standard deviation of the areas of those 5 pieces?
5.26ps.png
A. 2
B. √5
C. √6
D. √7
E. 2√2
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Re: v

by Max@Math Revolution » Thu May 28, 2020 2:00 am
=>
5.26ps(a).png
The areas of those 5 pieces are 1, 3, 5, 7, and 9, and their average is 3.
The variance is [(1-5)^2 + (3-5)^2 + (5-5)^2 + (7-5)^2 + (9-5)^2 ] / 5 = ( 16 + 4 + 0 + 4 + 16 ) / 5 = 40/5 = 8.
Then, the standard deviation is √8 = 2√2.

Therefore, the answer is E.
Answer: E
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