# Finding the Confidence Interval

1. Find the 90 percent confidence interval for the standard deviation of gasoline mileage mpg for these 16 San Francisco commuters driving hybrid gas-electric vehicles.

38.8 48.9 28.5 40.0 38.8 29.2 29.1 38.5

34.4 46.1 51.8 30.7 36.9 25.6 42.7 38.3

2. Biting an un-popped kernel of popcorn hurts! As an experiment, a self confessed connoisseur of cheap popcorn carefully counted 773 kernels and put them in a popper. After popping, the un-popped kernels were counted. There were 86. (a) Construct a 90 percent confidence interval for the proportion of all kernels that would not pop. (b) Check the normality assumption (c) Try the Very Quick rule. Does it work well here? Why, or why not? (d) Why might this sample not be typical?

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#### Solution Summary

This solution calculates the confidence intervals for two different situations.