125
iii.
Calculate the error bound.
f.
What does it mean to be “95% confident” in this problem?
Exercise 8.9
(Solution on p. 135.)
Suppose that 14 children were surveyed to determine how long they had to use training wheels.
It was revealed that they used them an average of 6 months with a sample standard deviation of
3 months. Assume that the underlying population distribution is normal.
a. i.
x
=
________
ii.
s
x
=
________
iii.
n
=
________
iv.
n

1
=
________
b.
Define the Random Variable
X
, in words.
c.
Define the Random Variable
X
, in words.
d.
Which distribution should you use for this problem? Explain your choice.
e.
Construct a 99% confidence interval for the population average length of time using training
wheels.
i.
State the confidence interval.
ii.
Sketch the graph.
iii.
Calculate the error bound.
f.
Why would the error bound change if the confidence level was lowered to 90%?
Exercise 8.10
Insurance companies are interested in knowing the population percent of drivers who always
buckle up before riding in a car.
a.
When designing a study to determine this population proportion, what is the minimum num
ber you would need to survey to be 95% confident that the population proportion is esti
mated to within 0.03?
b.
If it was later determined that it was important to be more than 95% confident and a new survey
was commissioned, how would that affect the minimum number you would need to survey?
Why?
Exercise 8.11
(Solution on p. 136.)
Suppose that the insurance companies did do a survey. They randomly surveyed 400 drivers and
found that 320 claimed to always buckle up. We are interested in the population proportion of
drivers who claim to always buckle up.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.