can any one help me with this math quistion?

Question

over the last 7 days mr smith spent the following number of hours readign a nocel: 3,1.5,2,1,5,4,2,5,3. find the standard deviation to the nearest tenth?

srry I made a mistake the #'s are 3, 1.5, 2, 1.5, 4, 2.5, 3

Answer 1

to find the standard deviation of
3,1.5,2,1,5,4,2,5,3

Find the mean (average) of the numbers, which is 2.94444444

Subtract the mean from each number, to get:
0.0555556, -1.44444, -0.944444, -1.94444, 2.05556, 1.05556, -0.944444, 2.05556, 0.0555556

Square each of these numbers, arriving at:
0.00308642, 2.08642, 0.891975, 3.78086, 4.22531, 1.1142, 0.891975, 4.22531, 0.00308642

Now add up all these numbers, and divide by (N-1), where N is the number of numbers. In this case, N = 9, so add them up and divide by 8, yielding:
2.15278

Now take the square root of this number, which gives you the standard deviation of:
1.46723