The following stem-and-leaf display shows, for a sample of U.S. states, the percent of the state's population that is 6 years or younger. For example, the smallest percentage is 15.4% and the largest is 21.9%.

Stem | Leaf

15 | 4

16 | 3 4 6 8

17 | 0 1 1 3 6

18 | 5

19 |

20 | 2

21 | 9

Calculate the mean, median and standard deviation.