Answers to 1.15, 1.25, 1.55 and 1.61 in back of the text

1.

a)
mean = .298
b)
standard deviation s = .0455
c)
mean = 0.3115
standard deviation s = .02206
d)
No. The population mean batting average is the average of all the major league ball players and will be lower than the mean batting average for the eight starters. They have been chosen for the All Star Team partly because they are good players.
e)
No. Since the members of the All Star Team are chosen for their batting ability we would expect most of them to have high batting averages. There would be less variability in batting averages for the All Star Team than for the major league ballplayers as a whole.

2.

a)
n=20
b) Relative frequency distribution for number of close friends


number of close friends x	frequency f	relative frequency f/n
0	2	0.10
1	3	0.15
2	5	0.25
3	5	0.25
4	4	0.20
5	1	0.05
total	20	1.00

c)
50% of the students had 2 or fewer close friends.
d)
mean = 2.45 median = 2.5 standard deviation s = 1.39

3. The conclusion is not valid since the sample on which it was based was probably biased toward parents who would not have children again if they had the choice. No random sampling was involved. People wrote in because they wanted to and these people were likely to have strong feelings on the subject. The parents who enjoyed their families were not motivated to write in.

More complete solutions to many of the practice problems from the text can be found in Study Guide for Moore and McCabe's Introduction to the Practice of Statistics

(available in Math/Stats Learning Centre)