Arithmetic Grade Four

Lesson One hundred and fifty-nine: Probability


We can talk about the probability of many different events. For instance, consider a six-sided die with sides labeled 1, 2, 3, 4, 5, and 6. The probability of rolling a 2 is 1 out of 6 since there is only 1 way of rolling a 2 and there are 6 possible outcomes. The probability of rolling and odd number (1, 3, or 5) is 3 out of 6 since there are 3 odd numbers which you could roll and 6 possible outcomes.

In this lesson we are going to discuss the probability of an arrow on a spinner landing on a section of a particular color. (Our pictures won't have any arrows though... so you can imagine arrows if you really want to.)

The following picture shows a spinner with 5 sections which are either yellow or red.

As you can see 3 sections are red and 2 are yellow. So the chances of landing on a red section are 3 out of 5 and the chances of landing on a yellow section are 2 out of 5.


Here's another example:

This time we have 10 sections.

We can answer questions like about this spinner:


  1) What is the probability of landing on a yellow section?
     ANSWER: 5 out of 10

  2) What is the probability of landing on a red section?
     ANSWER: 5 out of 10

  3) Which color is most likely to be selected?
     ANSWER:  Both are equally likely and so neither is more 
              likely to be selected.


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