95% of the math scores lie between what two values? (Give an
estimate
)
Use the 689599.7 Rule (aka Empirical Rule). About 95% of the scores lie within 2
standard deviations of the mean. That means 95% of the math scores lie between
702(10) and 70+2(10) = 50 and 90.
i.
Bob scores 85 on each exam. On which exam did he perform better,
compared to his classmates?
Compare Z scores
on the two exams. From part b, Bob’s Z score on the math exam
is 1.5. On the stat exam, Bob’s Z score is
= 1.0. Bob did better
on the math exam.
1
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2. Data are collected on the fuel economy of 2001 model midsize cars. The information
measured in average miles per gallon (MPG) is summarized below.
MPG
Frequency
32
30
28
26
24
22
7
6
5
4
3
2
1
0
Histogram of MPG
Descriptive Statistics: MPG
Total
Variable
Count
Mean
StDev
Minimum
Q1
Median
Q3
Maximum
MPG
32
26.750
2.874
22.000
24.000
26.500
28.750
33.000
Can the 689599.7 rule be applied to this data to give an approximate range
where 95% of the MPG lie? Explain why or why not.
No; data are not close to
a normal distribution
3. Bob’s Zscore on a psychology exam is 0.25. What is the correct interpretation?
a. Bob’s score is at the 25
th
percentile.
b. Bob got a 25 on the exam.
c. Bob’s score is 25 percentage points above the mean.
d. Bob’s score is 0.25 standard deviations above the mean.
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 Fall '11
 Johnson
 Statistics, Normal Distribution, Standard Deviation, ZScores, math exam

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