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S is standard deviation of a, b, and c, if a constant C is added to all the three digits, the new standard deviation will be?
A)S B)S* C)S*3C D)S+C E)S+3C
Source->E-gmat
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Dear stonecold,
I'm happy to respond.
The standard deviation is a measure of spread. Suppose the three numbers were {1, 3, 5}. There are certain gaps on the number line between those numbers, and the SD is a way of quantifying that pattern of gaps. Now, add 80 to all three. The new set is {81, 83, 85}. Think about the gaps between those new numbers on the number line: the pattern of gaps is exactly the same as it was for the original set. The new numbers are just as "spread apart" as were the original numbers. Therefore, the SD is the same.
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