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Statistics and Society 9/29/99
Practice Items on the Normal Distribution
1. Scores on a commonly used IQ test are
approximately normally distributed with mean 100
and standard deviation 15. In a group of 1000 people,
about how many would have IQ's above 115?
a) about 5
b) about 25
c) about 50
d) about 160 e) some other number
2. Here are two stemplots. What statistics are the most
appropriate (valid, not misleading) descriptive statistics
for the 'typical' members of the distributions represented
by these stemplots?
Stemplot I
Stemplot II
0
0
1
1
2
2
3
3
4
4
5
5
0
0
1
1
2
2
3
3
4
4
5
5
000000111112222333344
5567789
024
7
2
1
6
7
3
778
111233
555677799
000113344444
55566777788999
00000111222
555667
000
79
8
a) The mean is appropriate I, & the median for II.
b) The median is appropriate for I, & the mean for II.
c) The median is appropriate for I and for II.
d) The mean is appropriate for I and for II.
e) Both b) and c) are correct.
3. Scores on a commonly used IQ test are
approximately normally distributed with mean 100
and standard deviation 15. In a group of 1000 people,
about how many would have IQ's above 115?
a) about 5
b) about 25
c) about 50
d) about 160 e) some other number
4. Scores on a statistics test were approximately
normally distributed with mean 70 and standard
deviation 10. The instructor wants to give A's to the top
16 percent of the class. Use the 68/95 rule to determine
which scores should get A's?
a) 70 and up b) 75 and up
c) 80 and up
d) 84 and up e) 90 and up
5. Which of the following should not be used with
highly skewed data?
a) the 68/95 rule
c) a stem plot
e) both a) and d)
b) a five number summary
d) the median
6. Diastolic blood pressure readings for a sample of 200
men are approximately normally distributed with
mean 70. One hundred and thirty-six (136) of the men
had readings between 55 and 85. Use the 68/95 rule
to decide which of the following is closest to the
standard deviation of the blood pressure readings.
a) 1
b) 15
c) 30
d) 45
e) 90
7. Diastolic blood pressure readings for a sample of 200 men
are approximately normally distributed with mean 70. One
hundred and thirty-six (136) of the men had readings
between 55 and 85. Use the 68/95/99.7 rule to decide which
of the following is closest to the standard deviation of the
blood pressure readings.
a) 1
b) 15
c) 30
d) 45
e) 90