Statistics question for calculator...?

a car has a mean gas mileage of 53 miles per gal. the gas mileage of the car is approx. normally distributed with a standard deviation of 3.2 miles per gal.

A-)What is the 90th percentile of the gas mileage?

B-) What is the gas mileages that makes up the middle 92%?



the teacher emphasized that i needed to learn this on the calculator. i use a ti-89, so anyone know how to do a problem like this?Statistics question for calculator...?
Are you allowed to use a z-score chart? If so, 90th is closest to 1.29 on the z-score chart. z = observed minus mean divided by sd. By solving for the observed... If we times the z-score by the sd and then add the mean, we should get the 90th percentile. This comes out to be 57.13 miles per gal.



Does this make sense?

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