Hypothesis testing

[Kamal1]

In questions of the type:

Suppose a manufacturer makes a tool using an old process (mean defect rate 10%) and the standard deviation is 2. A new technology firm comes out with a process (mean sample defect rate 7%) with sample standard deviation of 1.8.

should we use the population standard deviation or the sample?

[Amit Goyal]

If you want the right answer post the complete question.

[Kamal1]

A tire manufacturer has been making snowtires. His test tyres has averaged 52,500 miles with a std deviation of 7,075. A new tread design is thought to add additional wear to the tires. Sixty tires with new process are tested revealing a mean of 54,112 miles, with a standard deviation of 7,912 miles. At the 5% level can it be said that the new tread adds to the wear.

Allen Webster chptr 8 question 68