Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: THEend8_
STATS 240 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
2 ,
(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
2
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
economist’s hypothesis.
Round intermediate steps to 4 decimal places and round to 3 decimal places.