In: Statistics and Probability
Sales personnel for Skillings Distributors submit weekly reports listing the customer contacts made during the week. A sample of 85 weekly reports showed a sample mean of 17.5 customer contacts per week. The sample standard deviation was 5.3. Provide 90% and 95% confidence intervals for the population mean number of weekly customer contacts for the sales personnel.
A. 90% Confidence interval, to 2 decimals:
(___,____)
B. 95% Confidence interval, to 2 decimals:
(__,___)
Solution :
Given that,
A.
t
/2,df = 1.663
Margin of error = E = t/2,df
* (s /
n)
= 1.663 * (5.3 /
85)
Margin of error = E = 0.96
The 90% confidence interval estimate of the population mean is,
- E <
<
+ E
17.5 - 0.96 <
< 17.5 + 0.96
16.54 <
< 18.46
90% Confidence interval is (16.54 , 18.46)
B.
t
/2,df = 1.989
Margin of error = E = t/2,df
* (s /
n)
= 1.989 * (5.3 /
85)
Margin of error = E = 1.14
The 95% confidence interval estimate of the population mean is,
- E <
<
+ E
17.5 - 1.14 <
< 17.5 + 1.14
16.36 <
< 18.61
95% Confidence interval is (16.36 , 18.61)