# Calculate Missing Probability Values

In this worksheet, students will calculate missing probability values and find the probability of an event not happening.

Key stage:  KS 3

Curriculum topic:   Probability

Curriculum subtopic:   Enumerate Sets Using Tables, Grids and Diagrams

Difficulty level:

#### Worksheet Overview

This activity will focus on finding missing probability values.

Important info: The probability of all possible outcomes adds up to 1 (or 100%)

Example

The probability of landing on each colour of a spinner is shown in the table below:

Find the probability of the spinner landing on yellow.

Reminder: all the probabilities in this table must add up to 1.

Let's start by adding the three existing probabilities together. As they all have different denominators, let's start by finding a common denominator.

1/4 x 10 = 10/40

3/8 x 5 = 15/40

1/5 x 8 = 8/40

10/40 + 15/40 + 8/40 = 33/40

Therefore 1 or 40/40 - 33/40 = 7/40

This fraction cannot be simplified, therefore the probability of landing on yellow must be 7/40

Let's try some questions.

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