Stat 1000 Tips for Assignments about Probability
Published: Thu, 10/21/10
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Tips for Assignments about Probability
For those of you using Web Assign these tips refer to HW5. If you are taking the course by distance/online, these tips relate to your HW7. If you are doing good old-fashioned paper hand-in assignments, these tips will help you with the second half of Assignment 3; you will also want to see my tips on Density Curves and the Normal Distribution that I will sent earlier this week.
Study Lesson 5 in Volume 2 of my book, if you have it, to prepare for this assignment.
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. 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.
I think they are quite clear what to do in Web Assign's 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.
In Web Assign question 5, you are dealing with a density curve. Be sure to review the first couple of questions in Lesson 2 of my book to better understand what is going on here.
Those of you doing the old-fashioned hand-in assignment, note that question 3 is best solved using a Venn Diagram.