Probability+of+a+Single+Event

Directions: 1. Read the notes on Probability below and write the important information and examples into your notes. 2. At the end, open the document called "Probability Regents Problems" and complete the worksheet. Turn in your work during class.

As discussed in Lesson 2: Intro to Probability, probability is a fraction and in order to write the fraction we need to know the number of favorable outcomes and the total number of outcomes. Once we know this information, we can substitute the numbers into the the fraction:
 * NOTES:**

Most of the problems we will see involving probability will be word problems. Therefore, the most important part of solving a probability problem is breaking down the word problem to determine:

a) What event is the problem talking about? (Right now, we will only be discussing problems with 1 event. In the next 3 lessons, we will discuss how to solve probability problems that have more than 1 event) b) What is the favorable outcome? c) How many favorable outcomes are there? d) How many total outcomes are there?

Once we know this information, we can write the fraction that represents the probability.

//Example: Three high school juniors, Reese, Matthew, and Chris are running for student council president. A survey is taken a week before the election asking 40 students which candidate they will vote for in the election. The results are shown in the table below: //

Based on the table, what is the probability that a student will vote for Reese?
 * ~ Candidate's Name ||~ Number of Votes ||
 * = Reese ||= 15 ||
 * = Matthew ||= 13 ||
 * = Chris ||= 12 ||

To answer this problem, we need to know: What event is the problem talking about? Casting one vote for student council president What is the favorable outcome? Voting for Reese How many favorable outcomes are there? 15 How many total outcomes are there? 40

Now that we know this information, we can write the probability:

//Example 2:// Now that we know that the probability of Reese getting a vote is 3/8, how could we find the probability that the student does NOT vote for Reese?

This could be done 2 different ways:

Method 1 - We know that the probability of all the outcomes together is 1. We know that the probability of Reese getting a vote is 3/8. Therefore, the probability of Reese NOT getting a vote is:

Method 2 - Now that the problem has changed, our new favorable outcome is Reese NOT getting a vote (or in other words, Matthew or Chris getting a vote). Therefore, our new number of favorable outcomes is 25, but our total number of outcomes has not changed. Now we can write out the probability as a fraction:



PRACTICE: