In: Statistics and Probability
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)84.87
B)88.83
C)86.83
D)30.89
E)89.56
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