Math Background

Probability: Tips and Tricks

  • Display in the classroom a large chart that shows a neat, orderly tree diagram listing outcomes from 2 or 3 sets. An example is shown below. This will provide a model for students to draw their own tree diagrams.
    tree diagram chart
  • When making an organized list or drawing a tree diagram to find all the possible outcomes of a probability experiment, have students check the number of outcomes by using multiplication to find the number of possible outcomes. For example, students should be able to list all the possible outcomes or draw a tree diagram for flipping a coin and then rolling a number cube. Before they begin to find all possible outcomes for those events, they should know that that there will be a total of 12 possible outcomes:
    2 (heads or tails for the coin) x 6 (numbers on the cube) = 12
  • Studying probability is a great opportunity to use manipulatives with your students. Demonstrate and let students model probability experiments and problems with as many coins, number cubes, spinners, marbles, and counters as possible. When a student rolls two number cubes 100 times and records the results in a table, the problem of finding the probability of rolling a sum of 4 will have much more relevance.
  • Point out to students that the probability of an event occurring plus the probability of the event not occurring should always total 1. When rolling a number cube (1-6), the probability of rolling a 3 is one-sixth. The probability of not rolling a 3 is five-sixths. one-sixth + five-sixths = 6/6 = 1.

Houghton Mifflin Math Grade 5