Question

A manager records the repair cost for 29 randomly selected washers. A sample mean of $84.87 and sample standard deviation of $12.34 are subsequently computed. Assume the population is normally distributed. Determine the upper endpoint of a 95% confidence interval estimate of the true mean repair cost.

A. 86.83

B. 84.87

C. 89.56

D. 30.89

E. 88.83

Answer 1

Solution :

sample size = n = 29

Degrees of freedom = df = n - 1 = 28

t /2,df = 2.048

Margin of error = E = t/2,df * (s /n)

= 2.048 * (12.34 / 29)

Margin of error = E = 4.69

The 95% confidence interval estimate of the population mean is,

- E < < + E

84.87 - 4.69 < < 84.87 + 4.69

80.18 < < 89.56

Upper endpoint = 89.56