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PS GMATPREP STANDARD DEVIATION
Source: Beat The GMAT — Problem Solving |
This is actually a lot easier than it seems. To decrease the standard deviation, we need to decrease the variation of the numbers. By adding more numbers at the mean, we will decrease the variation, and therefore the standard deviation. So, the answer is E, 6 and 6.
Jim S. | GMAT Instructor | Veritas Prep
Here is my reasoning for E:
Variance = (Sum of squares of deviations from mean)/N.
Now, the addition of 6 and 6 doesn't change the average.
It also doesn't change the sum of squares of deviations. But, it does change the denominator, N, which goes to 102. Therefore, the resulting variance, and hence SD is less than the original d.
However, I couldn't come up with an eifficient logic to eliminate the other choices. Any throughts on how to rule out the other answer choices?
Variance = (Sum of squares of deviations from mean)/N.
Now, the addition of 6 and 6 doesn't change the average.
It also doesn't change the sum of squares of deviations. But, it does change the denominator, N, which goes to 102. Therefore, the resulting variance, and hence SD is less than the original d.
However, I couldn't come up with an eifficient logic to eliminate the other choices. Any throughts on how to rule out the other answer choices?
