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Chapter 6 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
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
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.
An electric circuit is designed so that voltage
levels are uniformly distributed between
5.00V and 9.00V. Find the probability that a
randomly selected voltage level is between
7.00V and 8.50V.
.375
If heights of adult males are normally
distributed with a mean of 70.2 inches and a
standard deviation of 4.2 inches, and 95% of
all adult males satisfy a minimum height
requirement for police officers, what is that
minimum height requirement?
63.29 inches
Suppose that a distribution is shown to the
right.



P (x<1)=
P (x>2)
P (1<x<3)=
.25
.375
.75
In studying ocean conditions, the Bureau of
Fisheries found that for one location, the
August water temperatures (in degrees
Fahrenheit) were normally distributed with a
mean of 83.6 and a standard deviation of 2.4.
Find the temperature that is exceeded 10%
of the time.
86.68°F
A service station is located at one end of a 4kilometer tunnel. Any vehicle breakdown
requires servicing is equally likely to occur at
any point in the tunnel.
 What is the probability that a service call
will involve a vehicle located in the first 1.8
km?
 What is the probability that a service call
will involve a vehicle located at least
halfway in the tunnel?
a) .45
b) .5