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Standard deviation

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by BTGmoderatorRO » Fri Sep 15, 2017 1:28 pm
Which of the following sets has the smallest standard deviation?

A. {2, 5, 13, 17, 23}
B. {3, 4, 7, 18, 18}
C. {-50, 2, 33, 34, 35}
D. {1, 4, 12, 16, 17}
E. {0, 0, 0, 19, 31}

QA is d

can you please explain why option c is the correct answer.? or do you have an alternative answer to this
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by Jay@ManhattanReview » Tue Sep 19, 2017 1:11 am
Roland2rule wrote:Which of the following sets has the smallest standard deviation?

A. {2, 5, 13, 17, 23}
B. {3, 4, 7, 18, 18}
C. {-50, 2, 33, 34, 35}
D. {1, 4, 12, 16, 17}
E. {0, 0, 0, 19, 31}

QA is d

can you please explain why option c is the correct answer.? or do you have an alternative answer to this
Hi Roland2rule,

It would be nice if you write the source of questions. Is it a GMAT source?

The correct answer for this one is D, but it involves a lot of calculation which is not expected in the GMAT.

Computation of standard deviation (SD) is not within the scope of the GMAT; however, its analysis is within the scope. This question can be answered by analyzing the values.

Standard deviation is the measure of the spread of values of the set with respect to the mean of the set. Farther the values on either side of the mean, greater is the standard deviation and vice-versa.

In the given question, there are five sets and each set has five numbers. Ideally, we must first calculate the mean of each set and then find out the deviations. But this is going to take a lot of time.

Thought by analysis, we can eliminate option A, C, and E, choosing one option between B and D is difficult without computation, which is out of scope.

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