Stat 1000: Tips for Web Assign HW 07
Published: Sat, 03/26/11
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General Tips for Web Assign and JMP
When working with Web Assign, always enter the answer to one specific box and then click "Submit Answer" to confirm that is correct before you move on to another box. Do not enter several answers all at once in several boxes before you click "Submit Answer". You risk being marked wrong due to some typo or something.
For some strange reason, JMP 8 occasionally computes wrong answers even if you have copied and pasted your data correctly. I suggest that, if it is feasible, type the given data into your calculator (in Stat mode as shown in Appendix D of my book), and have your calculator compute the sample mean. Compare that answer with JMP's answer for the sample mean. If they are the same, everything is fine. If they are not the same, close JMP 8 and restart it, recopy and paste the data, and check again. Sometimes you have to do this 2 or 3 times before JMP finally works. If it is not feasible to use your calculator to compute the sample mean, have JMP do the question 2 or 3 times, being sure to restart JMP and recopy the data each time, and confirm that JMP gives you the same answer each time before risking entering the results into Web Assign.
If you are taking the course by distance/online (Section D01) click here to see your tips for HW 07.
Study Lesson 8 in my book, if
you have it, to prepare for this topic.
First, be sure to note
whether a question gives you σ, the population standard deviation, or s, the
sample standard deviation. That dictates whether you will use z or t when
making your confidence interval. I would assume, at this stage, you are likely
to be given σ most of the time.
Question 1 is standard
stuff. Note, the margin of error in a confidence interval is everything after
the "+/-". Take a look at question 10 in my Lesson 8 for an example of how to deal with an unusual level of confidence.
Question 3 requires you to use algebra to work backwards from the confidence limits to determine what they want. This will be quite challenging for many of you, but you could use trial and error. In part (a), try, for example z* for 95% confidence and see if that works. If not, you can tell if you need to try a higher or lower confidence, and just work from there. Part (b) is harder because the unknown is sigma(x-bar), the standard deviation of x-bar. Realize that the margin of error, m, is z* times sigma(x-bar), so you can solve sigma(x-bar) by algebra.
Question 4 is just more standard confidence interval stuff.
Question 5 requires you to copy and paste the
data into JMP 8. Click "New Data Table", then select "Edit"
then "Paste with Column Names". Now select "Analyze", "Distribution" and
highlight "DRP" and click "Y, Columns", then click OK. You are now looking at a
histogram and stuff. Click the red triangle next to "DRP" then select
"Confidence Interval" from the drop-down list. Select "Other" to get a pop-up
menu. It probably already has 0.95 typed in (for 95% confidence interval), but,
if not, be sure to type in 0.95. Make sure you click the box saying
"Use known Sigma". Click "OK" and you will then get a pop-up menu to
type in the sigma value. I believe σ = 11 in your case. Click "OK" and JMP
gives you the Confidence Interval at the bottom of the printout.
You can now select, copy
and paste your output to a file ready for upload as usual. Remember to include an interpretation of the confidence interval as requested. I show you how to do that at the start of Lesson 8 and give you an example in my question 1 (b).
Study Lesson 5 in Volume 2 of my book, if you have it, to prepare for this assignment.
Question 1:
When you are asked to list sample spaces, generally you will use a two-way table to visualize all the possible outcomes. If you are asked to count the number of things (number of coins, number of successes, etc.), list the sample space from lowest possible number up. Don't forget that, when counting the possible number of things, there is always the chance that there could be 0 things. Some of you are asked about coins. Note, they are not asking you what denomination the coins are (pennies, nickels, dimes, etc.). That is irrelevant. They don't care what kind of coins you might have, just how many and how much money are they worth.
When they ask you, "Are the outcomes equally likely?", think carefully. Remember, to be equally likely means that the first outcome you have listed in your sample space, has the same probability of happening as the second outcome, etc. Don't think that because the outcomes are equally easy to list, that makes them equally likely.
For example, if I ask you to the list the sample space for the possible medals an Olympic athlete might win, I could say the sample space is {Gold, Silver, Bronze, No medal at all}. Even though there are four possible outcomes, they are not equally likely! There is not a 25% chance of winning a Gold medal, for example. It depends what athlete we are talking about, what event, etc. The mere fact I have to say "it depends" tells me the outcomes are not equally likely. Even if the actual medal someone won was randomly determined and we were assuming every person has an equal chance of winning, if there were 20 people competing for the medal, there would be only a 1/20 chance they would win gold (since only one person can win gold), and a 17/20 chance they win no medal at all. Of course, some athletes may be the favourite to win gold and they would then have a much higher chance than 1/20 of winning.
Of course, some outcomes are equally likely. For example, if you are flipping a fair coin, or rolling a fair die, you have every right to say either side of the coin or die are equally likely to come up.
I think they are quite clear what to do in question 2 which has you read digits off of Table B. When making your stemplot, consider all the 0s as 00s, all the 1s as 01s, all the 2s as 02s, etc. Then, as they say, you will have a 0 stem where you list all the 0 leaves, a 0 stem where you list all the 1 leaves, 0 stem where you list all the 2 leaves, etc. Trust the graph you make.
Questions 3 and 4 are quite similar to my questions in Lesson 5.
Question 5 is dealing with a density curve. Be sure to review the first two questions in Lesson 2 of my book to better understand what is going on here.
Question 6 is just more probability practise.