Homework 6 (35 points)
STAT 110
Name(s) ______SOLUTION_____________
Due: Tuesday, April 16th by 4pm
1. College students and surfers Rex Robinson and Sandy Hudson collected data on their selfreported number of days surfed in a month. The data can be found in the file surfing.jmp on
the course website. You must paste or provide a detailed sketch of the JMP output used to
answer each question. (2 points each)
a. Find the average (mean) number of days surfed in a month. Be sure to use the
appropriate statistical notation in your answer.
x = 10.08 days
b. Find the range for the number of days surfed in a month. Be sure to show how you
computed this value.
Range = max – min = 25 – 2 = 23 days
c. Between what two values do the middle 99% of days surfed in a month fall?
Between 2 and 25 days (i.e. between the 0.5th and 99.5th percentiles)
d. Using JMP, create a histogram for the number of days in surfed in a month. Paste or
provide a detailed sketch of your plot below.
e. Looking at the histogram created in part e, describe the shape (or distribution) for the
number of days surfed in a month.
Right Skewed
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f.
Using JMP, create a boxplot for the number of days surfed in a month. Paste or provide
a detailed sketch of your plot below.
g. Looking at the boxplot created in part f, are there any potential outliers in the data?
Explain.
Yes, because there are dots present in the boxplot.
2. According to a University of Florida wildlife ecology and conservation researcher, the average
level of mercury uptake in wading birds in the Everglades has declined over the past several
years (UF News, 2000). Five years ago the average level was 15 parts per million (ppm).
Research Question – Is there evidence that the average level of mercury uptake in
wading birds in the Everglades has declined over the past several years?
a. Set up the appropriate null and alternative hypotheses that would be used to test the
research question of interest. (2 points)
H0: µ ≥ 15
Ha: µ < 15
b. Describe a Type I error in context for this situation. (2 points)
Conclude that the average level of mercury uptake in wading birds in the
Everglades has declined over the past several years, when in actuality it has
not declined.
c. Describe a Type II error in context for this situation. (2 points)
Conclude the average level of mercury uptake in wading birds in the
Everglades has not declined over the past several years, when in actuality is
has declined.
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3. Recall the text messaging data used in class (messages.jmp).
a. Using JMP, find a 99% confidence interval for the true mean number of text
messages sent in a day by WSU students. Provide a detailed sketch of or paste your
JMP output below. (2 points)
81.24 ≤ µ ≤ 125.66
b. Interpret the 99% confidence interval found in part a. (3 points)
99% confident the true mean number of text messages WSU students send in
a day is between 81.24 and 125.66 messages.
4. A company that packages bags of horse carrots decides to randomly choose some of the
bags coming off the production line to make sure they contain the correct weight of carrots
which is 20 pounds. Using JMP, carry out a hypothesis test to answer the research question
given below. Make sure to clearly state your hypotheses, condition(s), test statistic, p-value,
and conclusion in context. Include a detailed sketch of or paste your JMP output used to
answer the question below. The data can be found in the file horse_carrots.jmp on the
course website. (10 points)
Research Question – Is there evidence that on average the bags contain fewer carrots
than they should?
H0: µ ≥ 20
Ha: µ < 20
Condition:


N = 19 < 30 so the sample size condition is not met
Need to check for normality – OK since the red & green lines
“match” and the points fall near/on the red reference line.
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t = 4.1153
p-value = 0.9997
No evidence that on average the bags of contain fewer carrots than they should.
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