A survey of 25 randomly selected customers found the ages shown(in years). The mean is 32.24 years and the standard deviation is 10.04 years.

a) Construct a 80% confidence interval for the mean age of allcustomers, assuming that the assumptions and conditions for the confidence interval have been met.

b) How large is the margin oferror?

c) How would the confidence interval change if you had assumed that the standard deviation was known to be 11.0 years?

23

26

45

21

46

30

38

31

46

22

34

28

23

34

48

39

36

36

20

30

12

32

42

18

46

a) What is the confidenceinterval?

( , )

(Round to two decimal places asneeded.)

b) What is the margin oferror?

The margin of error is

(Round to two decimal places asneeded.)

c) What is the confidence interval using the given population standarddeviation? Select the correct choice below and fill in the answer boxes within your choice.

(Round to two decimal places asneeded.)

A.

The new confidence interval ( , ) is narrower than the interval from part a.

B.

The new confidence interval ( , ) is wider than the interval from part a.