STA113: Probability and Statistics in Engineering

Frequently Asked Questions

1. When will the homework solutions be posted on the Web?
We'll try to have homework solutions posted within a few days of when they're due. That's one reason late homeworks aren't accepted.

2. Why can't I view the Homework Solutions on the web page?
Homework solutions are not posted until the assignments are due, of course. The Homework Solutions and some other items are in PostScript format; your web browser has to be set up correctly (so it will call GhostView as a "helper application") for you to view them. If yours isn't set up correctly you may still be able to SAVE the file and then PRINT it. Or try one of the UNIX, MAC, or PC cluster machines, which seem to work correctly on PostScript.

3. How do we turn in Minitab homework?
Please write up your solutions to each problem, including those on which you used Minitab (whether or not it was required). For Minitab assignments please also include only the page of Minitab output that has the results you need... circle or in some other way direct the graders' and my attention to the parts that you used.
Turning in just the Minitab output, without your description of the solution, is not acceptable.

4. How can we learn how to use Minitab? Will it be taught in class?
From the course home-page you can get to a (very short) introduction to how to start Minitab at Duke and get to the on-line help facility. You can also get help from your friends & classmates, your TA (both in office-hours and in recitation section), from the optional book Minitab Handbook by Ryan, Joyner, & Ryan (it's at the Duke bookstore), from the manual that comes with the personal (PC or Mac) versions of Minitab (also at the bookstore), from materials on Minitab's home web page (there's a link to it on the course home page), or from Minitab itself-- after starting Minitab, try typing HELP HELP to find out more about the on-line Minitab help system.

5. When are the Midterms, and what do they cover?
The first Midterm Examination is Thursday, February 19, in class. It covers all course material through Thursday, February 5; this includes Mendenhall & Sincich chapters 1-5. There is no homework assignment due (and no recitation section meeting) on Friday, February 20. It is a closed-book exam.

The second Midterm Examination is Thursday, April 2, in class. It covers all course material through Thursday, March 12; this includes Mendenhall & Sincich chapters 1-9. There is no homework assignment due (and no recitation section meeting) Friday, April 3. While some review material from chapters 1-5 may appear on the second midterm, expect most to be from chapters 6-9.

6. Can we bring a sheet of formulas to the Midterm?
Yes, you may bring a single one-sided 8½x11" sheet of formulas, definitions, etc. (this formula sheet may give you some ideas). I will include a normal distribution table just like Table 4, too and, for the second midterm, a table of the Student's t distribution just like Table 7.

7. Why aren't solution sets available for the old midterms and finals?
The most effective way to use old midterm and final exams as study aids is to try solving the problems, preferably without using notes or texts, to help you see what material you should spend more time studying. When solution sets or even just answers are available, many students find it impossible to resist looking at the solutions or answers without actually working through the problems' solutions; this completely wastes the value of having old exams made available. The TA's and professor will be happy to look over your solutions and discuss them with you, individually or in small groups, and will make extra time (not just office hours) to do this.

8. What are projects like? When are they due? How can we get a data set?
Look at the project link from the syllabus page.

9. I've gotten my Minitab program to run just fine, but how can I print the output?
You need to save your commands, tables, etc, to a file (using 'outfile' or 'save', for example), and then print the resulting file after you exit minitab. Try HELP OUTFILE or HELP SAVE; briefly, from within Minitab you type outfile 'myfile' to start saving both your input and Minitab's output to a file named 'myflie.LIS' (you can use any name you like, of course), and nooutfile to stop saving output; another outfile 'myfile' appends further output to the same file. After you stop minitab you can print the file from the Unix prompt by typing lpr myfile.LIS, possibly after first editing it with an editor like emacs or vi. Thus to save the output for Problem 1 of Homework Set 1, you could type:

    MTB> outfile 'prob1'
    MTB> random 20 c1-c25;
    SUBC> integers 1 365.
    MTB> tally c1-c25
    Continue?

    ... (25 tally counts omitted here)

    MTB> nooutfile
    MTB> stop

Then under the Unix prompt, please try:


    more prob1.LIS

to look through the resulting output file. You could use an editor (such as emacs or vi) to revise your file prob1.LIS and then print it using the Unix command


    lpr prob1.LIS

As an alternative, you might try the Minitab command paper, which will print your entire session, once you stop Minitab.

9. How can I use minitab to generate 500 observations from some discrete distribution?
In order to generate random samples from a discrete distribution that is not already in Minitab, we first need to tell Minitab about the distribution. Make two columns, one for the possible values y and the other for the corresponding probabilities p(y), then use the Minitab command discrete. For example, to generate a sample from a random variable Y taking the values 1, 2, 4 with probabilities .1, .5, .4 you could type:

    MTB > read c10 c11
    DATA> 1 0.10
    DATA> 2 0.50
    DATA> 4 0.40
    DATA> end
    3 rows read.
    MTB > random 500 c1;
    SUBC> discrete c10 c11.
    MTB >

Now c1 contains the sample; you can find its mean, view it, find a histogram, or whatever you like, using the usual commands mean c1, print c1, hist c1, etc.