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Current explanation implies one would calculate the stddev for the sequence.

Alternate explanation: They're all just skip+1 sets of the form f(n)=kn+x, k=2, no need to calculate stddev.

BELOW IS REVISED VERSION OF THIS QUESTION:

Which of the following sets has the standard deviation greater than the standard deviation of set X={-19, -17, -15, -13, -11}

I. A={1, 3, 5, 7, 9}

II. B={2, 4, 6, 8, 10}

III. C={1, -1, -3, -5, -7}

A. Set A only B. Set B only C. Set C only D. Sets A, B and C E. None of the sets

If we add or subtract a constant to each term in a set the standard deviation will not change.

Since each set can be obtained by adding some constant to each term of set X (20 for set A, 21 for set B and 12 for set C), then the standard deviations of all sets are the same.