The chance that something will happen


Students will:

1. learn what probability is,

2. learn different ways to express probability numerically: as a ratio, a decimal, and a percentage, and

3. learn how to solve problems based on probability.

How the lesson is taught.


1. Begin the lesson by asking students to define probability (the likelihood or chance that a given event will occur). Probability is usually expressed as a ratio of the number of likely outcomes compared with the total number of outcomes possible. Ask students if they can give an example of probability.

2. To help students understand probability, work on the following problem as a class: Imagine that you have boarded an airplane. The rows are numbered from 1 to 30, and there are six seats per row, three on each side of the isle. Seats in each row are labeled A through F. Using that information, work together as a class to solve the problems listed below.

  1. How many seats are in the airplane? 180 seats
  2. What are your chances of sitting in row number 7? 6/180, or 1/30
  3. What are your chances of sitting in a window seat? There are two window seats per aisle, for a total of 60 window seats. Your chances of seating at a window would be 60/180, or 1/3.
  4. What are your chances of sitting in an "A" seat? There are 30 A seats, so your chances are 30/180, or 1/6.
  5. What are your chances of sitting in an even-numbered row? Of the 30 rows, 15 are even-numbered, so your chances are 15/30, or 1/2.

3. To figure out each problem, students must set up a ratio between the total number of outcomes—in these problems either the total number of seats or rows—and the specific question asked.

Probability - Equal, Likely, Unlikely, Certain, Impossible - Grade 3 Math Lesson