GRE Subject Test: Math : Variance

Study concepts, example questions & explanations for GRE Subject Test: Math

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Example Questions

Example Question #33 : Other Topics

Find the variance of the scores 18, 4, 9, 6, 11, and 20.

Possible Answers:

\(\displaystyle 41.78\)

\(\displaystyle 34.56\)

\(\displaystyle 28.33\)

\(\displaystyle 43.09\)

\(\displaystyle 35.91\)

Correct answer:

\(\displaystyle 34.56\)

Explanation:

First find the mean of the scores by adding them up and dividing by the number of scores.

\(\displaystyle 18+4+9+6+11+20=68\)

\(\displaystyle \frac{68}{7}=11.33\)

Subtract the mean of 11.33 from each of the scores.

\(\displaystyle 18-11.33=6.67\)

\(\displaystyle 4-11.33=-7.33\)

\(\displaystyle 9-11.33=-2.33\)

\(\displaystyle 6-11.33=-5.33\)

\(\displaystyle 11-11.33=-0.33\)

\(\displaystyle 20-11.33=8.67\)

Now, square the results.

\(\displaystyle 6.67^{2}=44.49\)

\(\displaystyle (-7.33)^{2}=53.73\)

\(\displaystyle (-2.33)^{2}=5.43\)

\(\displaystyle (-5.33)^{2}=28.41\)

\(\displaystyle (-0.33)^{2}=0.11\)

\(\displaystyle 8.67^{2}=75.17\)

Now we need the average of these values to get the variance. First, add up these values.

\(\displaystyle 44.49+53.73+5.43+28.41+0.11+75.17=207.34\)

Now divide by 6 which is the number of scores.

\(\displaystyle \frac{207.34}{6}=34.56\)

Example Question #1 : Variance

\(\displaystyle What\ is\ the\ standard\ deviation\ for\ a\ set\ of\ data\ with\ a\ variance\ of\ 16?\)

Possible Answers:

\(\displaystyle 256\)

\(\displaystyle 16\)

\(\displaystyle 4\)

\(\displaystyle 8\)

Correct answer:

\(\displaystyle 4\)

Explanation:

\(\displaystyle The\ relationship\ between\ standard\ deviation\ and\ variance\ is\ listed\ below:\)

\(\displaystyle (standard\ deviation)^2=variance\)

or

\(\displaystyle standard\ deviation=\sqrt{variance}\)

\(\displaystyle In\ this\ question\ variance=16\)

\(\displaystyle This\ means\ that\ standard\ deviation=\sqrt{16}=4\)

 

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