Question

The yearly mileage accumulated by an automobile in a large car rental company’s fleet is normal with mean 18000 kilometres and standard deviation 1700 miles. At the end of the year the company sells 80% of its cars, keeping the 20% with the lowest mileage. Do you think a car whose year-end mileage is 17400 k.m. is likely to be kept?

Answer 1

This is just Z table stuff. You can play around with the values at

http://davidmlane.com/hyperstat/z_table.html

Answer 2

Another method.

Z = (score-mean)/SD = (17400-18000)/1700 = ?

Look in the back of your statistics textbook for a table called something like “area under normal distribution” to find the proportion/probability related to the Z score.