Question

A random sample of the costs of repair jobs at a large muffler repair shop produces a mean of $127. 95. And a standard deviation of $24. 3. If the size of this sample is 40, which of the following is an approximate 90 percent confidence interval for the average cost of a repair at this repair shop?.

Answer 1

The confidence interval for the average cost of a repair at this repair shop is $127.95\pm6.321$

Confidence interval

The formula for calculating the z-score is expressed as:

$CI = \overline x \pm z\frac{s}{\sqrt{n} }$

Given the following

• mean = 127. 95
• z = 1.645
• s = 24.3
• n = 40

Substitute the given parameters

$CI = 127.95 \pm 1.645*\frac{24.3}{\sqrt{40} }\\CI = 127.95 \pm 1.645*\frac{24.3}{6.324 }\\CI = 127.95 \pm 6.321$

Hence the confidence interval for the average cost of a repair at this repair shop is $127.95\pm6.321$

Learn more on confidence interval here: brainly.com/question/15712887