Practice Problems for Normal Distributions and Uniform Distributions
© 2010 Radha Bose FSU Department of Statistics
1
1.
Let us suppose that the times (in minutes) that people take to shower can be modeled by the U(5,60)
distribution.
(a) What is the mean shower time?
(b) Between which two values are the middle 50% of shower times?
(c) What percent of people take longer than 40 mins to shower?
(d) What percent of people take 40 mins to shower?
(e) Between which two values does the third quarter
of shower times fall?
(f) If 35% of us take longer to shower than you do, how long do you take to shower?
2.
The head circumferences of a certain animal are Uniformly distributed between 51 and 67 cm.
(a) Write down the notation for the distribution of head circumferences.
(b) What is the fivenumber summary of the distribution?
(c) Zoos generally look for animals with head circumferences between 56 and 62 cm.
What percent of the
total population consists of such animals?
(d) Animals who are not yet mature generally have head circumferences in the lower 20%.
If a research
biologist is looking for an immature animal, what is the maximum head circumference he should be looking
for?
3.
The times taken to drive from City A to City B can be modeled by a Normal distribution with mean 89
mins and standard deviation 13 mins.
(a) What is the distribution here?
(b) Draw an appropriately labeled density curve showing what the
Empirical rule
predicts about the
driving times.
(c) What percent of drivers take between 63 and 102 mins to drive from City A to City B?
(d) The 16
th
percentile of a distribution is a number that has 16% of the data less than or equal to it.
What is the 16
th
percentile of the driving times distribution?
4.
Let us suppose that the number of hours per week that prekindergarten children spend in daycare can
be described by a Normal model with mean 30 hours and standard deviation 7 hours.
(a) What is the distribution here?
(b) Draw an appropriately labeled density curve showing what the
Empirical rule
predicts about the
number of hours per week spent in daycare.
(c) What percent of prekindergarten children spend between 23 and 44 hours per week in daycare?
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 Fall '11
 RADHABOSE
 Normal Distribution, Standard Deviation, Radha Bose FSU Department of Statistics, Radha Bose FSU, Bose FSU Department

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