oss198 wrote:

If the standard deviation of Set Y is 4, what are the greatest and least values that are within one standard deviation of the mean?

(1) The median of Set Y is 5.

(2) The mean of Set Y is 6.

Standard deviation is how spread out the number are from the mean. The question asked for the greatest and least values that are within one standard deviation of the mean, reading from the question only, we know that we need the mean to calculate values.

(2) mean = 6, then greatest value = 6+4 = 10, least value = 6-4 = 2

(2) is sufficient. B is the answer.

As for (1), the median has nothing to do with standard deviation, so we can eliminate (1).

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