Chapter 7 Review

1
Chapter 7 Review
2

• A z-score is
• The mean of the distribution
• The deviation from the mean divided by the
  standard deviation
• Always positive
• The standard error

3

• The mean score on a certain mathematics aptitude
  test is 72, with a standard deviation of 8.5.
  Assume a normal distribution of scores. If a
  student's z-score on the test is known to have
  been at the 25th percentile, what was the
  students actual score?
• 66.267

4

• The life of Sunshine Stereo CD players is
  normally distributed with a mean of 2.3 years and
  a standard deviation of 0.4 year. What
  proportion of the players will break during the
  guarantee period of 2 years?
• 0.2266

5

• From the previous question, P(X lt 2) 0.2266.
  If the store sells 10 of these CD players on a
  given day, what is the probability that at least
  3 of the players will break during the guarantee
  period of 2 years?
• 0.4033

6

• Suppose the average score on a national test is
  500 with a standard deviation of 100. If each
  score is increased by 25, what are the new mean
  and standard deviation?
• m 625 s 125

7

• The mean score on a certain mathematics test is
  72 with a standard deviation of 8.5. Assume a
  normal distribution of scores. What score would
  one have to earn so that no more than 15 of the
  scores would be higher?
• 80.81

8

• Suppose you toss a die with 3 red sides, 2 white
  sides, and 1 blue side. What is the probability
  that the first toss that lands blue is the 5th
  toss?
• .0804

9

• In a recent study it was found that in one town
  the number of hours that a typical 10-year-old
  child watches television per week is evenly
  distributed with a median of 12 hours and a
  maximum of 15.5 hours. If Gary is a typical
  10-year-old in this town, what is the probability
  that he watches between 9 and 14 hours?
• 0.7143

10

• A traffic control engineer has found that the
  waiting time for a commuter in the Parker Road
  toll plaza of North Dallas Tollway during rush
  hour is approximately uniformly distributed with
  a mean of 8.7 minutes and a range of 5 minutes.
  What is the probability that the a randomly
  selected commuter will have to wait more than 10
  minutes?
• 0.24

11

• Which of the following statements are true?
• The area under a normal curve is always equal to
  1, no matter what the mean and standard deviation
  are.
• The larger the standard deviation of a normal
  curve, the taller and thinner the curve.
• Normal curves with different means are centered
  around different numbers.

T
F
T
12

• A Cornell University researcher measured the
  mouth volumes of men and women. She found a mean
  of 66 cc for men (s 17 cc) and a mean of 54 cc
  for women (s 14.5 cc). If the distribution of
  mouth volumes is approximately normal, what is
  the probability that the difference in volumes
  (male female) is at least 59 cc?
• .0179