Use Probability to Find Missing Values

Are you ready to work backwards?

In this activity, you will need to use probability to help to find missing values.

Example

A bag contains some counters. There are 6 red, 7 green and some yellow counters. 

The probability of choosing a counter and it being red is 6/17.

How many yellow counters are there?

This tells us that there are 17 counters altogether. We can use this information to then work out how many yellow counters there must be:

6 red + 7 green = 13 counters

17 - 13 = 4

There must be 4 yellow counters in the bag.

Let's use our detecting skills to answer some questions now.