Answer:
For this distribution of test scores, the standard deviation is equal to the square root of 9
D) 9
Explanation:
We need to know the standard deviation formula:
(1)
Where:
S: Standard deviation
sum: Summation
x: Sample values
Am: Arithmetic mean
n: Number of terms, in this case 3
Now, we need to know the arithmetic mean of the sample values: 2, 5 and 8

To know the standard deviation we need to have the summation of each term minus the arithmetic mean squared.
of each term:

Now, we can find the standard deviation:

The standard deviation is equal to the square root of 9