Suppose that a city is made up of three counties Washington

Suppose that a city is made up of three counties: Washington County, Adams County, and Jefferson County. Among the commuters who live in Washington County, 25 percent have a commute to work of at least 30 minutes, while 75 percent have a commute to work of less than 30 minutes. Similarly, among commuters who live in Adams County, 25 percent have a commute to work of at least 30 minutes, while 75 percent have a commute to work of less than 30 minutes. Suppose that 60 percent of commuters who live in the city have a commute to work of less than 30 minutes, and suppose that half of the commuters in the city live in Jefferson County. Among commuters who live in Jefferson County, find the percent that have a commute to work of at least 30 minutes.

Solution

Let there are 200 people in the city. Consider the following table.

Washington + Adams

Jefferson

Total

At least 30 min.

25

55

80

Less than 30 min.

75

45

120

100

100

200

Therefore, among commuters, who live in Jefferson county, the percent that have a commute to work of at least 30 minutes is 55%.