20.1 Number of children. The Census Bureau gives this distribution for the number of a household’s related children under the age of 18 in American households in 2011:
| Number of children: | 0 | 1 | 2 | 3 | 4 |
| Proportion: | 0.67 | 0.14 | 0.12 | 0.05 | 0.02 |
In this table, 4 actually represents four or more. But for purposes of this exercise, assume that it means only households with exactly four children under the age of 18. This is also the probability distribution for the number of children under 18 in a randomly chosen household. The expected value of this distribution is the average number of children under 18 in a household. What is this expected value?