HW Help Stats
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hw_stats_4-5.docxIllowsky Chapter, #60
Use the following information to answer the next two exercises: The patient recovery time from a particular surgical procedure is normally distributed with a mean of 5.3 days and a standard deviation of 2.1 days.
What is the median recovery time?
a. 2.7
b. 5.3
c. 7.4
d. 2.1
Illowsky Chapter 6, #66
Height and weight are two measurements used to track a child’s development. TheWorld Health Organization measures child development by comparing the weights of children who are the same height and the same gender. In 2009, weights for all 80 cm girls in the reference population had a mean μ = 10.2 kg and standard deviation σ = 0.8 kg. Weights are normally distributed. X ~ N(10.2, 0.8). Calculate the z-scores that correspond to the following weights and interpret them.
a. 11 kg
b. 7.9 kg
c. 12.2 kg
Illowsky Chapter, #88
Facebook provides a variety of statistics on its Web site that detail the growth and popularity of the site.
On average, 28 percent of 18 to 34 year olds check their Facebook profiles before getting out of bed in the morning. Suppose
this percentage follows a normal distribution with a standard deviation of five percent.
CHAPTER 6 | THE NORMAL DISTRIBUTION 365
a. Find the probability that the percent of 18 to 34-year-olds who check Facebook before getting out of bed in the
morning is at least 30.
b. Find the 95th percentile, and express it in a sentence.
Illowsky Chapter , #70
Which of the following is NOT TRUE about the distribution for averages?
a. The mean, median, and mode are equal.
b. The area under the curve is one.
c. The curve never touches the x-axis.
d. The curve is skewed to the right.
Lane Chapter , #12
Use the normal distribution to approximate the binomial distribution and find
the probability of getting 15 to 18 heads out of 25 flips. Compare this to what
you get when you calculate the probability using the binomial distribution.
Write your answers out to four decimal places.
Lane, Chapter 10, #4
Why is a 99% confidence interval wider than a 95% confidence interval?
Lane, Chapter 10, #12
A person claims to be able to predict the outcome of flipping a coin. This
person is correct 16/25 times. Compute the 95% confidence interval on the
proportion of times this person can predict coin flips correctly. What
conclusion can you draw about this test of his ability to predict the future?
Lane, Chapter 10, #18
You were interested in how long the average psychology major at your college studies per night, so you asked 10 psychology majors to tell you the amount they study.
They told you the following times: 2, 1.5, 3, 2, 3.5, 1, 0.5, 3, 2, 4.
(a) Find the 95% confidence interval on the population mean.
(b) Find the 90% confidence interval on the population mean.
Illowsky, Chapter 8, #100
What is meant by the term “90% confident” when constructing a confidence interval for a mean?
a. If we took repeated samples, approximately 90% of the samples would produce the same confidence interval.
b. If we took repeated samples, approximately 90% of the confidence intervals calculated from those samples would
contain the sample mean.
c. If we took repeated samples, approximately 90% of the confidence intervals calculated from those samples would
contain the true value of the population mean.
d. If we took repeated samples, the sample mean would equal the population mean in approximately 90% of the
samples.
Illowsky, Chapter 8, #116
random sample of size 12 to check the amount of soda served in the 16 oz. serving size. The sample mean is 13.30 with a
sample standard deviation of 1.55. Assume the underlying population is normally distributed.
What is the error bound?
a. 0.87
b. 1.98
c. 0.99
d. 1.74
