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Substitute Decimal Numbers into Algebraic Expressions

In this worksheet, students will substitute decimal numbers for letters and work out the value of simple expressions with two variables.

'Substitute Decimal Numbers into Algebraic Expressions' worksheet

Key stage:  KS 3

Year:  Year 8 Maths worksheets

Curriculum topic:   Algebra

Curriculum subtopic:   Substitute Numerical Values for Formulae/Expressions

Popular topics:   Algebra worksheets, Decimals worksheets

Difficulty level:  

Worksheet Overview

When we substitute a number for a letter, we simply replace the letter with the number.


However, we must remember that 4b means 4 x b.



Work out the value of the following expression when a = 4 and b = -0.5

3a - 7 - 2b



3a - 7- 2b

= (3 x a) - 7 - (2 x b)

= (3 x 4) - 7 - (2 x -0.5)

= 12 - 7 - (-1)

= 12 - 7 + 1

= 6


It is easy to get muddled with negative and positive signs if we're not careful, so make sure you remember the rules!


For multiplication and division:

One negative and one positive make a negative.

Two negatives make a positive!


When adding or subtracting:

One negative and one positive sign next to each other mean subtract.

Two negative signs next to each other mean add.


Let's have a go at some questions.


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