B use the 68 95 997 rule to find the proportion of

(b) Use the 68 – 95 – 99.7 rule to find the proportion of applicants whose score is between 338
and 853.
(c) What proportion of GRE scores are below 500?
(d) What proportion of GRE scores are above 800?
(e) Calculate and interpret the 34th per centile of the distribution of applicants’ GRE scores.

72 The Practice of Statistics, 4/e- Chapter 2 © 2011 BFW Publishers
2. (a) Find the proportion of observations from a standard Normal distribution that satisfies
0.51 < Z < 2.84. Sketch the Normal curve and shade the area under the curve that is the
answer to the question.
(b) What z -score in a Normal distribution has 22% of all scores above it?
3. A Normal probability plot for the weights of 40 squirrels trapped and released on a college
campus is shown below. Is the distribution of squirrel weights approximately Normal?
Justify your answer.
26 25 24 23 22 21 20 19 18
2
1
0
-1
-2
Squirrel weight (oz.)
z-Score

© 2011 BFW Publishers The Practice of Statistics, 4/e- Chapter 2 73
Quiz 2.2C AP Statistics Name:
1. Approximate the median, mean, and standard deviation of the Normal distribution graphed
below.
Median: __________
Mean: __________
Standard Deviation: __________
2. The scores of a reference population on the Wechsler Intelligence Scale for Children (WISC)
are approximately Normally distributed with μ = 100 and V = 15.
(a) What score would represent the 50th percentile? Explain.
(b) A score in what range would represent the top 1% of the scores?
(c) What proportion of the reference population has WISC scores below 110?
(d) What proportion of the reference population has WISC scores between 80 and 110?
450 400 350 300 250 200 150 100 50 0 -50 -100
Score

74 The Practice of Statistics, 4/e- Chapter 2 © 2011 BFW Publishers
3. The weights of healthy adult male Labrador Retrievers are approximately Normally
distributed with a mean of 77 pounds and a standard deviation of 6 pounds. What is the
interquartile range of male Labrador weights?
4. Twenty students were asked to guess the age of a man in a photograph. Here are their
guesses:
44 43 48 37 44 40 33 42
50 49 43 46 46 45 43 38
Are these guesses approximately Normally distributed? Provide evidence to support your
answer.
43 41
39 41

Test 2A AP Statistics Name:
Part 1: Multiple Choice. Circle the letter corresponding to the best answer.
1. The heights of American men aged 18 to 24 are approximately Normally distributed with a
mean of 68 inches and a standard deviation of 2.5 inches. Only about 5% of young men have
heights outside the range
© 2011 BFW Publishers The Practice of Statistics, 4/e- Chapter 2 75