9.61 The average thickness of the plastic coating on electrical wire is an important variable in determining the wearing characteristics of the wire.

Ten thickness measurements from randomly selected points along a wire gave the following

(in thousandths of an inch):

Construct a 99% tolerance interval for 95% of the population measurements on coating thickness.

What assumption is necessary for your answer to be valid?

8, 7, 10, 5, 12, 9, 8, 7, 9, 10