Sales personnel for skillings distributors submit weekly reports listing the customer contacts made during the week. a sample of 65 weekly reports showed a sample mean of 19.5 customer contacts per week. the sample standard deviation was 5.2. provide 90% and 95% confidence intervals for the population mean number of weekly customer contacts for the sales personnel.

As per given , we have

sample size : n= 65

degree of freedom : df=n-1=64

sample mean :

sample standard deviation : s= 5.2

Since , the population standard deviation is not given  , so we apply t-test.

Significance level  for 90% confidence :

t-critical value for significance level 0.10 and df = 64 would be :

Formula for Confidence interval :

Then , 90%  confidence intervals for the population mean number of weekly customer contacts for the sales personnel would be :

∴ 90% confidence intervals for the population mean number of weekly customer contacts for the sales personnel : (18.424, 20.576)

Significance level  for 95% confidence :

t-critical value for significance level 0.05 and df = 64 would be :

Then , 95%  confidence intervals for the population mean number of weekly customer contacts for the sales personnel would be :

∴ 95% confidence intervals for the population mean number of weekly customer contacts for the sales personnel : (18.212, 20.788)

i think it might be a but you might want a second opinion

6e14 is the answer.