Question

Most companies have increased their dependence on computers and software. As a result, more employee time is spent on the telephone with technical support for the software. A sample of 8 times spent on the phone with technical support yielded the following data:

Time spent on phone (in minutes)
11
9
9
8
12
13
11
14

Construct a 98 percent confidence interval estimate of the true mean population time that is spent by employees on the telephone with technical support for the software. Use only the appropriate formula and/or statistical table in your textbook to answer this question. Negative values should be indicated by a minus sign. Report your answers to 2 decimal places, using conventional rounding rules.

Answer: $ _____≤ (Click to select) ≤ $____

Answer 1

Solution:

Given: A sample of 8 times spent on the phone with technical support yielded the following data:

Time spent on phone (in minutes)
11
9
9
8
12
13
11
14

We have to construct a 98 percent confidence interval estimate of the true mean population time that is spent by employees on the telephone with technical support for the software.

Formula:

where

Thus we need to make following table:

x : Time spent on phone (in minutes)	x^2
11	121
9	81
9	81
8	64
12	144
13	169
11	121
14	196

Thus

and

t_c is t critical value for c = 98% confidence level

Thus find two tail area = 1 - c = 1 - 0.98 = 0.02

df = n - 1 = 8 - 1 = 7

Thus from t table for df = 7 and two tail area = 0.02

t_c = 2.998

Thus margin of error = E is

Thus

Thus a 98% confidence interval estimate of the true mean population time that is spent by employees on the telephone with technical support for the software is between