Question

A consumer group claims that wireless companies are worsening their customer service, with the time customers are kept on hold when contacting the company reaching an average of 4.4 minutes. You collect data on 40 random customer service calls and find that the sample mean time a customer is kept on hold is 4.5 minutes and standard deviation is 51 seconds (0.85 minutes). Develop a 95% confidence interval for the mean time customers are kept on hold.

Upper Bound: 4.79, Lower Bound: 4.21
	Upper Bound: 4.98, Lower Bound: 4.78
	Upper Bound: 5.45, Lower Bound: 3.02
	Upper Bound: 7.25, Lower Bound: 4.01

Answer 1

Solution :

sample size = n = 40

Degrees of freedom = df = n - 1 = 40 - 1 = 39

t _/2,df = 2.023

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

= 2.023 * (0.85 / 40)

Margin of error = E = 0.29

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

- E < < + E

4.5 - 0.29 < < 4.5 + 0.29

4.21 < < 4.79

Upper bound = 4.79

Lower bound = 4.21