GRE Quantitative Reasoning - Standard Deviation

The first step with standard deviation is to find the average or mean of the numbers. Add 3+5+8+9+10 together to get 35. Divide that by the number of scores, which is 5, to get a mean of 7.

Now, subtract the mean from each of the numbers

$\3-7=-4 \5-7=-2 \8-7=1 \9-7=2 \10-7=3$

Next, square those values

$(-4)^{2}=16$

$(-2)^{2}=4$

$1^{2}=1$

$2^{2}=4$

$3^{2}=9$

Now find the mean of these squared differences by adding the values and then dividing by the amount of numbers, 5 in this case.

$\frac{34}{5}=6.8$

Finally, take the square root of this number to get the standard deviation.

$\sqrt{6.8$

Standard Deviation

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