Download Statistics Chapter 9 Sections 1 and 2 Test 1. To select the correct

Statistics
Chapter 9 Sections 1 and 2 Test
1. To select the correct Student's t-distribution requires knowing the degrees of freedom.
How many degrees of freedom are there for a sample of size n?
x
a.) n – 1
b.) n
c.) n + 1
d.)
s
n
2. Suppose a 95% confidence interval for μ turns out to be 130    300 . To make
more useful inferences from the data, it is desired to reduce the width of the confidence
interval. Which of the following will result in a reduced interval width?
A) Increase the sample size.
B) Increase the sample size and decrease the confidence level.
C) Decrease the confidence level.
D) All of these.
3. Consider the following statements concerning confidence intervals:
A. A disadvantage of point estimates, when compared to interval estimates, is that the
increased precision achieved through taking a larger sample is not reflected in these
estimates
B. For a given sample size and population standard deviation, an increase in the
confidence level will make the interval narrower.
C. The only requirement for being able to use the standard normal distribution table to
obtain the critical value for a confidence interval estimate for the population mean is that
the sample size be large
(a)
(b)
(c)
(d)
(e)
only A is true
only C is true
only A and B are true
only B and C are true
none of A, B and C are true
4. Find the critical t-value that corresponds to 95% confidence and n = 16.
6. A random sample of 10 parking meters in a resort community showed the following
incomes for a day. Assume the incomes are normally distributed. Find the 95%
confidence interval for the true mean.
$3.60 $4.50 $2.80 $6.30 $2.60 $5.20 $6.75 $4.25 $8.00 $3.00
Clothing for runners. Your company sells exercise clothing and equipment on the
Internet. To design the clothing, you collect data on the physical characteristics of your
different types of customers. Here are the weights (in kilograms) for a sample of 24 male
runners. Suppose the standard deviation of the population is known to be 4.5 kg.
67.8 61.9 63.0 53.1 62.3 59.7 55.4 58.9 60.9 69.2 63.7 68.3 64.7 65.6 56.0 57.8
66.0 62.9 53.6 65.0 55.8 60.4 69.3 61.7
(a) What is the standard deviation of x-bar?
(b) Give a 95% confidence interval for µ, the mean of the population from which the
sample is drawn.
(The sample mean is 61.79, to save you some time).
A company that produces white bread is concerned about the distribution of the amount
of sodium in its bread. The company takes a simple random sample of 100 slices of
bread and computes the sample mean to be 103 milligrams of sodium per slice.
Construct a 99% confidence interval for the unknown mean sodium level
assuming that the population standard deviation is 10 milligrams.