A telephone counseling service for adolescents tested whether the length of calls would be affected by a special telephone system that had a better sound quality. Over the past several years, the lengths of telephone calls (in minutes) were normally distributed with

=19

and

=7.

The service arranged to have the special phone system loaned to them for one day. On that day, the mean length of the

45

calls they received was

22

minutes. Test whether the length of calls has changed using the 5% significance level. Complete parts (a) through (d).

A) Assume that the distribution of means is approximately normal. What are the cutoff sample scores on the comparison distribution at which the null hypothesis should be rejected?

-1.96, 1.96

B) Determine the sample's Z score on the comparison distribution.

Z=

C) Figure the 95% confidence interval. one can be 95% confident that the true population mean is between ______ and ______.

Can someone help me figure B) an C) please?