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Chapter 7 Review
A z-score is:
a)
b)
c)
d)
The mean of the distribution
The deviation from the mean divided
by the standard deviation
Always positive
The standard error
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 student’s actual score?
66.267
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
From the previous question, P(X < 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
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
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
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
In a recent study it was found that in one
town the number of hours that a typical 10year-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
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
Which of the following statements are
true?
a) The area under a normal curve is
T always equal to 1, no matter what the
mean and standard deviation are.
b) The larger the standard deviation of a
normal curve, the taller and thinner the
F
curve.
c) Normal curves with different means are
T centered around different numbers.
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