# Substitution with Decimal Numbers

In this worksheet, students substitute decimal numbers for letters and work out the value of simple expressions with two variables. Key stage:  KS 3

Curriculum topic:   Algebra

Curriculum subtopic:   Substitute Numerical Values for Formulae/Expressions

Difficulty level:   ### QUESTION 1 of 10

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 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

Work out the value of the following expression when a = 5.6 and b = 1

20 + 2a - b

Work out the value of the following expression when a = 0.75 and b = 2

20 + 2a - 3b

Work out the value of the following expression when a = 1.5 and b = 2

5a + 2 - b

Work out the value of the following expression when a = 0.8 and b = 1.5

2 - 2a + 2b

Work out the value of the following expression when a = 0.4 and b = 0.5

10 - 2a + b

Work out the value of the following expression when a = 9.9 and b = 1.1

20 - a + b

Work out the value of the following expression when a = 0.1 and b = 0.5

2a + 5 - 2b

Work out the value of the following expression when a = 0.2 and b = 2

2a + 6 - 3b

Work out the value of the following expression when a = 4.4 and b = 0.5

2a - 7 + 3b

Work out the value of the following expression when a = 2.7 and b = -0.5

a + a + b

• Question 1

Work out the value of the following expression when a = 5.6 and b = 1

20 + 2a - b

30.2
EDDIE SAYS
20 + (2 x a) - b 20 + (2 X 5.6) - 1 20 + 11.2 - 1 30.2
• Question 2

Work out the value of the following expression when a = 0.75 and b = 2

20 + 2a - 3b

15.5
EDDIE SAYS
20 + (2 x a) - ( 3 x b) 20 + (2 x 0.75) - (3 x 2) 20 + (1.5) - (6) 15.5
• Question 3

Work out the value of the following expression when a = 1.5 and b = 2

5a + 2 - b

7.5
EDDIE SAYS
(5 x a) + 2 - (b) (5 x 1.5) + 2 - (2) 7.5 + 2 - 2 7.5
• Question 4

Work out the value of the following expression when a = 0.8 and b = 1.5

2 - 2a + 2b

3.4
EDDIE SAYS
2 - (2 x a) + (2 x b) 2 - (2 x 0.8) + (2 x 1.5) 2 - 1.6 + 3 3.4
• Question 5

Work out the value of the following expression when a = 0.4 and b = 0.5

10 - 2a + b

9.7
EDDIE SAYS
10 - (2 x a) + (b) 10 - (2 x 0.4) + (0.5) 10 - 0.8 + 0.5 9.7
• Question 6

Work out the value of the following expression when a = 9.9 and b = 1.1

20 - a + b

11.2
EDDIE SAYS
20 - (a) + (b) 20 - (9.9) + (1.1) 11.2
• Question 7

Work out the value of the following expression when a = 0.1 and b = 0.5

2a + 5 - 2b

4.2
EDDIE SAYS
(2 x a) + 5 - (2 x b) (2 x 0.1) + 5 - (2 x 0.5) 0.2 + 5 - 1 4.2
• Question 8

Work out the value of the following expression when a = 0.2 and b = 2

2a + 6 - 3b

0.4
EDDIE SAYS
(2 x a) + 6 - (3 x b) (2 x 0.2) + 6 - (3 x 2) 0.4 + 6 - 6 0.4
• Question 9

Work out the value of the following expression when a = 4.4 and b = 0.5

2a - 7 + 3b

3.3
EDDIE SAYS
(2 x a) - 7 + (3 x b) (2 x 4.4) - 7 + (3 x 0.5) 8.8 - 7 + 1.5 3.3
• Question 10

Work out the value of the following expression when a = 2.7 and b = -0.5

a + a + b

4.9
EDDIE SAYS
(a) + (a) + (b) (2.7) + (2.7) + (-0.5) 2.7 + 2.7 - 0.5 4.9
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