Data Sufficiency (DS) | Re: Is the standard deviation of the numbers X, Y and Z equal to

Target question: Is the standard deviation (SD) of the numbers X, Y and Z equal to the standard deviation of 10,15 and 20?

IMPORTANT CONCEPT: In order for the SD of X, Y and Z to be equal to the SD of {10, 15, 20}, X, Y and Zmust have the same dispersion as {10, 15, 20}
That is, if X, Y and Z are arranged in ascending order, the 2nd value must be 5 greater than
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