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# Probability Part A: Probability in Statistics (20 minutes)

In This Part: What Is Probability?

Problem A1
Make a list of the topics and ideas that come to mind when you think of probability, including both everyday uses of probability and mathematical or school uses. Problem A2
What does probability have to do with statistics? Think about ways that statistics might use probability, and vice versa. Video Segment
In this video segment, participants discuss probability and how it relates to statistics. Watch this segment after recording your own thoughts on Problems A1 and A2.

When many people think of probability, they think of rolling dice, picking numbers at random, or playing the lottery. In fact, games of chance, which often involve dice or other random devices, rely on the principles of probability.

Problem A3
What is a random event? Give an example of something that happens randomly and something that does not. In This Part: A Game of Chance?

Can you improve the odds of a game with practice, or is it truly just a question of randomness? Let’s explore this question by playing Push Penny. See Note 2 below.

Make the Push Penny board by adding horizontal lines to a 36″ x 24″ sheet of poster board. (Despite its name, this game uses quarters rather than pennies, since they tend to slide better than other coins when pushed.) Draw the lines exactly two coin diameters apart, as illustrated below — uniform spacing on the lined poster board is crucial for meaningful analysis and interpretation of the results. Put the board on a flat surface, with a second sheet of blank poster board in front of it. To play, push a quarter from the edge of the blank board onto the lined board. Each round of the game consists of four pushes. You score a “hit” if the quarter touches one of the lines when it stops. You “miss” if the quarter stops between the lines. (Remove the coin from the board between successive pushes.)

Problem A4
Suppose you wanted to find out whether you could develop skill at playing rounds of Push Penny. How might you design an experiment to test this idea?

Problem A5
Play 20 rounds of Push Penny (four pushes per round), and record your results from each round using the following format (five rounds are provided as an example): a. Do the results from your 20 rounds suggest that you have developed skill in playing Push Penny?  Describe the process you used to answer this question.
b.
If you don’t think you’ve developed much skill in playing the game, do you think it is still possible to  develop this skill?
c.
Give an example of a game where it is not possible to increase your game-playing skills.

We will investigate Push Penny in more detail later in this session.

### Notes

Note 2
The primary problem of Session 8 is based on the question, “After several practices of Push Penny, have you developed skill in playing the game?”

This is a statistics problem; appropriate data consist of the results from several rounds of the game. The ultimate goal of this session is to compare the experimental results with the expected results, using a probability model.

First, you play 20 games and record the results from each game. Next, you consider whether the results indicate that you are a skillful Push Penny player. You then analyze the results for a person who played 100 games of Push Penny. Finally, based on these data, you try to determine whether the player did, in fact, develop any Push Penny skills.

Make sure that you allow time to develop your own ideas for analysis. In considering whether skill has been demonstrated, you may want to look at the average score or at the proportion of hits from all 400 pushes.

Both the average score and the proportion of hits depend on basic probability concepts. In order to determine whether the proportion of hits demonstrates skill, you must first consider the probability that a random push will hit a line. The “average” score depends on a concept of average other than the arithmetic mean: In this case, it is a weighted mean where the weights are probabilities.

The method of analysis investigated in this session — “goodness of fit” — uses the binomial probability model. At this point, it is important to consider how probability can be used in the analysis of this problem. You will return to the problem of determining skill after considering some basic ideas about probability.

### Solutions

Problem A1
Answers will vary. Some everyday uses of probability are predicting the weather, deciding which road is likely to have the least amount of traffic, and choosing a restaurant on the basis of how long you think the wait will be. Some mathematical uses include the probability of rolling a six on a die, the probability of tossing a coin and getting “heads,” and the probability of 1-2-3 coming up as the daily lottery number.

Problem A2
Statistical uses of probability include the probability that the estimate of a mean is accurate (this is known as a confidence interval). Places where probability uses statistics include taking experimental data and trying to create exact probabilities to match your data set.

Problem A3
A “random” event is entirely up to chance; there is no skill involved. A random event might be what appears as the top card after a thorough shuffling of a deck of cards. Most events are not random; for example, answering a question correctly on a test may happen randomly (as a guess) but usually is a result of skill.

Problem A4
You might look at your average score and determine whether your average score is improving over time. For example, if you played Push Penny 20 times a day for several days, you could compare your average first day’s score to your average last day’s score and see if there was any improvement.

Problem A5
a.