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Standard Deviation - GMAT prep

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by Stuart@KaplanGMAT » Sun Nov 22, 2009 3:21 pm
We know that 1 standard deviation is 22.4; to answer the question, we need to find the mean of the set.

Average = sum of terms/# of terms = (70+75+80+85+90+105+105+130+130+130)/10

If we want to keep the numbers small, we can divide by 10 before summing the 10 terms:

Avg = 7 + 7.5 + 8 + 8.5 + 9 + 10.5 + 10.5 + 13 + 13 + 13

Avg = 100

If one SD is 22.4, then 1 SD below the mean is 100 - 22.4 = 77.6

There are two times below 77.6: choose B.
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