EXAMPLE 7 Finding and interpreting the margin of error

In Example 5, the interval for the population mean city gas mileage for all motor vehicles is:

  1. Find the margin of error .
  2. Express the confidence interval in the form “point estimate ± margin of error”
  3. Interpret the margin of error .

Solution

  1. We find the margin of error as follows:

  2. The point estimate is . Thus, the 95% confidence interval for the population mean city gas mileage for all motor vehicles takes the following form:

  3. We interpret the margin of error by saying that we can estimate the population mean city gas mileage for all vehicles to within 0.93 mpg with 90% confidence.

NOW YOU CAN DO

Exercises 35–42.