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Yates et al - The Practice of Statistics 2/e (Homework)

James Finch

Statistics, section 2, Fall 2019

Instructor: Dr. Friendly

Current Score : 9 / 20

Due : Sunday, January 27, 2030 23:30 EST

Last Saved : n/a Saving...  ()

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4/5 0/6 –/2 2/4 3/3
Total
9/20 (45.0%)

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    Here are some textbook questions from The Practice of Statistics 2/e by Yates, Moore, and Starnes published by W. H. Freeman. Click here for a list of all of the questions coded in WebAssign. This demo assignment allows many submissions and allows you to try another version of the same question for practice.

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1. 4/5 points  |  Previous Answers YMSStat2 1.E.017. My Notes
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1/1 1/1 1/1 1/1 0/1
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4/5
 
The following figure is a histogram of the number of days in the month of April on which the temperature fell below freezing at Greenwich, England. The data cover a period of 65 years.

(a) Describe the shape of this distribution.
     Correct: Your answer is correct.
Describe the center of this distribution.
     Correct: Your answer is correct.
Describe the spread of this distribution.
     Correct: Your answer is correct.
Are there any outliers?
     Correct: Your answer is correct.

(b) In what percent of these 65 years did the temperature never fall below freezing in April?
Incorrect: Your answer is incorrect. %
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2. 0/6 points  |  Previous Answers YMSStat2 3.E.054. My Notes
Question Part
Points
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1 2 3 4 5 6
–/1 0/1 –/1 –/1 –/1 0/1
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0/6
 
Keeping water supplies clean requires regular measurement of levels of pollutants. The measurements are indirect - a typical analysis involves forming a dye by a chemical reaction with the dissolved pollutant, then passing light through the solution and measuring its "absorbence." To calibrate such measurements, the laboratory measures known standard solutions and uses regression to relate absorbence to pollutant concentration. This is usually done every day. Here is one series of data on the absorbence for different levels of nitrates. Nitrates are measured in milligrams per liter of water.
Nitrates5050100200 400800120016002000 2000
Absorbence7.07.512.8 24.047.094.0140.0182.0233.0228.0
(a) Chemical theory says that these data should lie on a striaght line. If the correlation is not at least 0.997, something went wrong and the calibration procedure is repeated. Plot the data. (Do this on paper. Your instructor may ask you to turn in this work.) Find the correlation.
r = Must the calibration be done again?
     Incorrect: Your answer is incorrect.


(b) What is the equation of the least-squares line for predicting absorbence from concentration?
Absorbence = + Concentration
If the lab analyzed a specimen with 700 milligrams of nitrates per liter, what do you expect the absorbence to be?
Based on your plot and your correlation, do you expect your predicted absorbence to be very accurate?
    
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3. –/2 points YMSStat2 4.E.022. My Notes
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1 2
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–/2
 
It is easy to measure the "diameter at breast height" of a tree. It's hard to measure the total "aboveground biomass" of a tree, because to do this you must cut and weigh the tree. The biomass is important for studies of ecology, so ecologists commonly estimate it using a power law. Combining data on 378 trees in tropical rain forests gives this relationship between biomass y measured in kilograms and diameter x measured in centimeters.
loge(y) = -2.4 + 2.42 loge(x)
Note that the investigators chose to use natural logarithms, with base e = 2.71828, rather than common logarithms with base 10.
(a) Translate the line given into a power model. Use the fact that for natural logarithms the following is true.
y = eloge(y)
y = Click here to preview your answer.
(b) Estimate the biomass of a tropical tree 33 centimeters in diameter.
kg
Click here for help with symbolic formatting.
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4. 2/4 points  |  Previous Answers YMSStat2 8.E.008. My Notes
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1 2 3 4
1/1 1/1 0/1 0/1
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2/4
 
Among employed women, 30% have never been married. Select 15 employed women at random.
(a) The number in your sample who have never been married has a binomial distribution. What are n and p?
n = Correct: Your answer is correct.
p = Correct: Your answer is correct.

(b) What is the probability that exactly 2 of the 15 women in your sample have never been married?
Incorrect: Your answer is incorrect.

(c) What is the probability that 2 or fewer women have never been married?
Incorrect: Your answer is incorrect.
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5. 3/3 points  |  Previous Answers YMSStat2 10.E.042. My Notes
Question Part
Points
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1 2 3
1/1 1/1 1/1
1/50 1/50 1/50
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3/3
 
To determine whether the mean nicotine content of a brand of cigarettes is greater than the advertised value of 1.4 milligrams, a health advocacy group test the following hypotheses.
H0: μ = 1.4
Ha: = 1.4
The calculated value of the test statistic is z = 2.73.
(a) Is the result significant at the 5% level?
     Correct: Your answer is correct.

(b) Is the result significant at the 1% level?
     Correct: Your answer is correct.

(c) By comparing z with the critical values in the bottom row of Table C, give two numbers that catch the P-value between them.
     Correct: Your answer is correct.
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