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

Next, square those values

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

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