A new process is being proposed for the manufacture of automobile tires. The manufacturing company is interested in constructing a 90% confidence interval for the rate of tread wear for tires manufactured using the new process.
(a) An initial sample of size 25 results in x =8 mm/10,000 miles and s = 2.5 mm/10,000 miles. Construct the desired interval.
(b) If the company is interested in obtaining a 90% confidence interval with margin of error 0.5 mm/10,000 miles, how many additional observations would be needed?