EXAMPLE 3 How many vehicles per household?
What is the average number of motor vehicles in American households? The Census Bureau tells us that the distribution of vehicles per household (based on the 2010 census) is as follows:
| Number of vehicles: | 0 | 1 | 2 | 3 | 4 | 5 |
| Proportion of households: |
0.09 | 0.34 | 0.37 | 0.14 | 0.05 | 0.01 |
This is a probability model for choosing a household at random and counting its vehicles. (We ignored the very few households with more than five vehicles.) The expected value for this model is the average number of vehicles per household. This average is
expected value = (0)(0.09) + (1)(0.34) + (2)(0.37)
+ (3)(0.14) + (4)(0.05) + (5)(0.01)
= 1.75 vehicles per household