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Calculate Missing Probability Values

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

'Calculate Missing Probability Values' worksheet

Key stage:  KS 3

Year:  Year 8 Maths worksheets

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%)



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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