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Substitution with Decimal Numbers

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

'Substitution with Decimal Numbers' worksheet

Key stage:  KS 3

Curriculum topic:   Algebra

Curriculum subtopic:   Substitute Numerical Values for Formulae/Expressions

Difficulty level:  

Worksheet Overview

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

 

Answer

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

CORRECT ANSWER
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

CORRECT ANSWER
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

CORRECT ANSWER
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

CORRECT ANSWER
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

 

CORRECT ANSWER
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

CORRECT ANSWER
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

CORRECT ANSWER
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

CORRECT ANSWER
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

CORRECT ANSWER
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

CORRECT ANSWER
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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