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Use Simple Algebraic Substitution with Negative Numbers

In this worksheet, students will substitute negative numbers for letters and work out the value of simple expressions with one variable.

'Use Simple Algebraic Substitution with Negative Numbers' worksheet

Key stage:  KS 3

Year:  Year 7 Maths worksheets

Curriculum topic:   Algebra

Curriculum subtopic:   Substitute Numerical Values for Formulae/Expressions

Popular topics:   Algebra worksheets, Year 7 Algebra 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.

 

Example

Work out the value of the following expression when a = 4

3a - 7

 

Answer

3a - 7

3a just means 3 x a , so we have

3 x a - 7

 

Change the letter (a) into the number we've been given (4)

3 x 4 - 7

 

Now multiply first - remember the order of BIDMAS (or BODMAS)

12 - 7 = 5

 

 

Sometimes we have a negative number to substitute and then we need to be very careful about the correct signs!

 

 

Example

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

3a - 7

 

Answer

3a - 7

3a just means 3 x a , so we have

3 x a - 7

 

Change the letter (a) into the number we've been given (-4)

3 x -4 - 7

 

Now multiply first - remember the order of BIDMAS (or BODMAS)

3 x -4 = -12

 

Finally, subtract 7:

-12 - 7 = -19

 

When working with negatives, it's important to remember the rules! 

 

Two negative signs next to each other means a positive.

One negative and one positive next to each other means a negative.

 

If we multiply or divide one positive and one negative, we get a negative.

If we multiply two positives or two negatives, we get a positive.

 

Are you happy with this?

 

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