STATS 240 Exam 2 Spring 2021
STATS 240 – Section __
1. Box final answers.
2. Neatly show details of work for full credit and to allow the possibility of partial credit.
3. Calculators are allowed on this exam. You may not share calculators. You may not
communicate with people other than your professor during this exam.
1. [10pts] The number of chocolate chips in a bag of Chips Ahoy! Chocolate chip
cookies are approximately normally distributed, with a mean of 1262 chips and a
standard deviation of 118 chips. Find the number of chocolate chips that make the
90th percentile of the number of chocolate chips in the bag.
Note: Choose ONE problem from #2 and #3. You don’t have to do both problems.
2. [10pts] Despite its nutritional value, seafood is only a tiny part of the American diet,
with the average American eating just 16 pounds of seafood per year with a
standard deviation of 3.2 pounds. Janice takes a random sample of 42 Americans.
Find the probability that the sample mean seafood consumption of the 42
Americans is more than 17.5 pounds? Use 4 non-zero decimal places in your
calculations. Round z-values to 2 decimal places.
3. [10pts] According to a study done by Wakefield Research, the proportion of
Americans who can order a meal in a foreign language is 47%. Suppose a random
sample of 200 Americans is taken, find the probability that the sample proportion
of Americans who can order a meal in a foreign language is less than 55%? Use 4
non-zero decimal places in your calculations. Round z-values to 2 decimal places.
4. [20pts] A random sample of 30 Suffolk University employees had an average
commute length of 11.7 miles, with a standard deviation of 8.5 miles. What is the
90% confidence interval for the mean commute length of all Suffolk employees?
Use 4 non-zero decimal places in your calculations.
(a) Find the α
(b) Find σ
(c) Find the margin of error (MoE) and construct the confidence interval
5. [20 pts] In a random poll taken in 2008, Gallup asked 1006 national adults whether
they were baseball fans. 433 of the sample said they were. Construct a 95%
confidence interval to estimate the proportion of national adults who are baseball
fans. Use 4 non-zero decimal places in your calculations.
a) Find the α
b) Find σ
c) Find the margin of error (MoE) and construct the confidence interval
6. [20pts] The rate of reported dreaming in color that was established in the 1940s
was 30%. Some researchers believe that the rate has been increased. A recent study
of dreaming found that out of a random sample of 113 people, 37 reported dreaming
in color. Use the significant level of 5% to test the researcher’s claim.
(a) State the null and alternative hypotheses. Specify the type of test.
(b) Compute the test statistic Round intermediate steps to 4 decimal places and
round to 2 decimal places.
(c) Use the z table to find the P-value
(d) What is your decision? Show detailed comparison and explanation.
7. [10pts] In 2001, the mean household expenditure for energy was $1493, according
to data from the U.S. Energy Information Administration. An economist wants to test
whether this amount has changed significantly from its 2001 level. In a random
sample of 35 households, he found the mean expenditure for energy during the most
recent year to be $1618, with a standard deviation $321. Conduct a hypothesis test
at 10% significance level to see whether we have strong evidence to support the
Round intermediate steps to 4 decimal places and round to 3 decimal places. 学霸联盟