Stat 1000: Tips for Assignment 3

Published: Tue, 02/18/14

Do note that my second midterm seminar is the weekend  of Mar. 8 and 9.  Click here for more details:
Did you read my tips on how to study and learn Stat 1000?  If not, here is a link to those important suggestions:
Did you read my Calculator Tips?  If not, here is a link to those important suggestions:
Did you read my Tips for Assignment 1?  If not, here is a link to those important suggestions:
Did you read my Tips for Assignment 2?  If not, here is a link to those important suggestions:
Tips for Assignment 3
You will have to study both Lesson 4: Density Curves and the Normal Distribution and Lesson 5: Introduction to Probability in my Basic Stats 1 book to prepare for this assignment.  Questions 1, 2, 3 and 4 cover the concepts I teach in Lesson 4.  The remaining questions are dealt with in Lesson 5 of my book.  Note: if you are using an older edition of my book, you may find that Density Curves and the Normal Distribution is Lesson 2.
Don't have my book?  You can download a free sample of my book and audio lectures containing Lesson 1:
A Warning about StatsPortal
Make sure that you are using Firefox for your browser.  Don't even use Internet Explorer.  It actually also has some glitches in the HTML editor boxes.

Do note that every time you exit a question in StatsPortal, the next time you return to it, the data may very well change.  Do not press the "back-up" button on your browser in a question.  That, too, will change the data.  When you are prepared to actually do a question, open the link, keep it open, and do not close it until you have submitted your answers.  Be sure to press "Save Answers" once you have done any calculations and entered any information to ensure the data does not change and force you to start over again.

After you submit the answer to a question, if you have been marked wrong on any parts, be sure that you write down the correct answers before you exit the screen (or grab a screen shot).  To try a second attempt at the question do not click the link to the question again, that will change the data and you will have to start all over again.  Also, DO NOT click "try again" or make a "second attempt."  That will also reset the data.

Instead, exit back to the home screen where they show the links for all the different questions on the assignment.  Where it shows the tries for a question on the right side of your screen, you should see the "1" grayed out, showing that you have had 1 attempt.  Click the number "2" to get your second attempt with the same data.  That way you can enter the answers you already know are correct and focus on correcting your mistakes.

You should also have already downloaded the JMP statistical software which was provided with either one of the course options for StatsPortal as mentioned in your course outline.

Make sure you have gone through Assignment 0 completely to learn how to use the interface.  I also suggest you print out a copy of question 8 in Assignment 0 (Long Answer Questions - Part 3) so that you have the steps for saving and uploading files into the HTML editor in front of you.
Question 1
This question is very similar to my question 2 in Lesson 4.  In part (e) you will have to work backwards.  You know the area, so you can establish what the width of the shaded region must be because you know the width times the height equals the area.  Then, you can establish what b must be knowing that Right - Left gives you the width.  In part (f), remember that the quartiles are splitting the area up into 25% sections.  Just slice the rectangle into four equal pieces.
Question 2
I strongly recommend you read my section in Lesson 4 about the Z Bell Curve Ladder and the X Bell Curve Ladder and make the ladder every single time you have a bell curve problem.  Then climb up or down the rungs.  Many students are guilty of not thinking a problem through, and consequently looking at Table A too soon.  The ladder trains you to focus on the fact that Table A deals with z scores and Left Areas, but your problem may be interested in something else.

You will be using Table A for much of this lesson.  Here is a link where you can download the table if you have not already done so:

This is very similar to my Lesson 4, question 5.
Question 3
This is very similar to my Lesson 4, question 6.  For part (g), that I also do a percentile example in my question 7.  As I say in my question 7, the 80th percentile, for example, is the z score that has 80% of the area to the left of that score.
Question 4
Make sure you have studied all my X-Bell Curve problems (questions 9 to the end) in Lesson 4 before you attempt this question.  Make sure you use the X-Bell Curve Ladder to help you work your way through each part of this question.

You also need to know the 68-95-99.7 Rule taught earlier in my lesson (questions 3 and 4 in Lesson 4).

Part (f) is all about z scores.  The higher your z score in a normal distribution, the better you did relative to others.  See my question 14 in Lesson 4 for an example of this principle.
Question 5
More X-Bell Curve stuff.  Note that you are to round off your answer in part (a) for mu, the population mean, to two decimal places.  You will then need that answer to help solve the remaining parts of the question.
Question 6
As they imply, the graph you want to make here is a normal quantile plot.  This is a scatterplot that compares the data scores to their standardized z scores.  If the normal quantile plot looks linear (JMP will draw the best fit line through the plot), then it is reasonable to assume the population is normal.  If the dots do not fit the line very well (if they look curved), that would suggest the population is not normal.
To make the normal quantile plot for part (a):
First, enter the data into JMP manually: Click the "New Data Table" icon on the toolbar at top left in the JMP home screen (or select "File" in the toolbar, then New, then Data Table).  You are automatically taken to an empty spreadsheet with one column. Double-click "Column 1" and change its name to "Weights", or right-click "Column 1" and select "Column Info" and type in the name "Weights" and click OK. 

Make sure the column properties are correct!  When you are naming the column, check what it says for Data Type and Modeling Type.  The Data Type should be numeric and the Modeling Type should be continuous.  If they are not, click the drop-down lists to change them.

Now enter the data you have been given down the column.  Note you can use your arrow buttons or TAB button to move from one cell to the next as you enter your data.

Once you have entered all the data down your columns, you are ready to make your normal quantile plot.  In the toolbar at the top, select Analyze then select Distribution.  In the "Select Columns" part of the pop-up window, click the column name to highlight it, and click the Y, Columns button.  You should see the column name appear in the section to the right of the "Y, Columns" button.  Click OK.

It now opens yet another pop-up window called "Distributions" where a histogram and other graphs should appear.  Click the red triangle next to "Weights" and select Normal Quantile Plot to get the graph you desire.

You are told to hide all the other parts of the output.  Click that same red triangle again and deselect "Outlier Box Plot" and anything else that has a check mark next to it.  Click the red triangle again, and select "Histogram Options" and deselect "Histogram" to make it disappear.  Click the red triangle again, select "Display Options" and  deselect "Quantiles" and "Summary Statistics" to make those parts disappear.  Alternatively, you can make the Quantiles and Summary Statistics disappear if you simply click the gray triangles (to the left of the red triangles) next to their title bars.  Click the gray triangles again to make them reappear.

You are now ready to insert your normal quantile plot into the HTML editor box:
  • If you are using Windows:
  • Press "Alt" on your keyboard or click the thin blue line that is near the top of the window to get the toolbar icons to appear.  Select "File" then "Save As" to get a pop-up window.  Type in whatever name you want the file to have in the "File name" section. Click the "Browse Folders" arrow and select which folder you want to save the file in (I suggest you select "Desktop" so that the file will just appear right on your desktop home screen).  Finally, click the drop down arrow in the "Save as type" section and select "JPEG File".  Click "Save".  You should now have your file ready to upload into the assignment.
  • To upload your file into the text box they provide: Click "HTML editor" below the text box (if you have not already done so) to make a toolbar appear in the text box.  Click the toolbar option called "Link" and select "Image."  In the pop-up window that appears, click the button called "Find/Upload File" (it is at the bottom of the pop-up window, you may have to enlarge the box or scroll down to see it).  Click the "Browse" button and find the histogram file you just saved.  Either double-click that file or select it and click "Open" and you should see the path to that file appear in the Browse box.  Click "Upload File" and its name should appear in the "Uploaded Files" pop-up window.  Select the file in the list of "Uploaded Files" to highlight it and click OK and you should see the file appear in the text box. 

  • If you are using Apple/Mac:
  • You will need to take a screen shot of your output in order to upload it.  To take a screen shot hold down Command+Shift+4 and drag the cross-hairs over the image to capture it.  The image will save a .png file to your desktop by default.
  • To upload your file into the text box they provide: Click "HTML editor" below the text box (if you have not already done so) to make a toolbar appear in the text box.  Click the toolbar option called "Link" and select "Image."  In the pop-up window that appears, click the button called "Find/Upload File" (it is at the bottom of the pop-up window, you may have to enlarge the box or scroll down to see it).  Click the "Browse" button and find the histogram file you just saved.  Either double-click that file or select it and click "Open" and you should see the path to that file appear in the Browse box.  Click "Upload File" and its name should appear in the "Uploaded Files" pop-up window.  Select the file in the list of "Uploaded Files" to highlight it and click OK and you should see the file appear in the text box.
Type your answer for part (b) into the box they provide.  Don't forget to click the HTML editor link first.
Question 7
Don't forget to click the Html Editor link before you type your answers into their box.

I show you how to determine a Sample Space through the use of two-way tables if necessary in Lesson 5 of my book.  Note that all you are asked for is the sample space in each part, so your answer would be something like this (don't forget to use those squiggly brackets "{}"):

Here is the sample space for the outcome of flipping a coin twice where H=heads and T=tails:  {HH, HT, TH, HH}.
Question 8
This is a question best solved by Venn Diagrams.  Make sure you have studied that section in  Lesson 5 my book and have done questions 14 to 18 before you attempt this question.  This question is similar to my question 16.