Within how many standard deviations of the mean do all of the values fall 11 14 10 8 12 13 12 18 9 12 16 15 11 9 10

The mean is 12 and std dev 2.8

The max is 18 and min is 8

One std dev would be:

If you add 2.8 + 12 = 14.8

If you subtract 12-2.8 = 9.2

Two std dev would be:

14.8 + 2.8 = 17.6

9.2-2.8 = 6.4

All of the data falls within 2 std deviations to the left and 3 std deviations to the right of the mean.