# Substitution (1)

In this worksheet, students substitute 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 = -5

3a - 7 - 2b

3a - 7- 2b

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

= (3 x 4) - 7 - (2 x -5)

= (12) - 7 - (-10)

= 12 - 7 + 10

= 15

Work out the value of the following expression when a = 7 and b = 2

20 - 2a + 5b

Work out the value of the following expression when a = 7 and b = 3

20 + 2a - b

Work out the value of the following expression when a = 10 and b = -3

20 + 2a - b

Work out the value of the following expression when a = 10 and b = 0

5a + a + 42b

Work out the value of the following expression when a = 10 and b = 4

3b + 5a + 2 + a

Work out the value of the following expression when a = 8 and b = -3

b + 24 - 2a

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

10 - 2a - b

Work out the value of the following expression when a = 4 and b = 2

2a + 5 - 3b

Work out the value of the following expression when a = 7 and b = -2

2a + 6 + 5b

Work out the value of the following expression when a = 4 and b = -2

2a - 7 - 3b

• Question 1

Work out the value of the following expression when a = 7 and b = 2

20 - 2a + 5b

16
EDDIE SAYS
20 - 2a + 5b 20 - (2 x a) + (5 x b) 20 - (2 x 7) + (5 x 2) 20 - 14 + 10 16
• Question 2

Work out the value of the following expression when a = 7 and b = 3

20 + 2a - b

31
EDDIE SAYS
20 + 2a - b 20 + (2 x a) - b 20 + (2 x 7) - 3 20 + 14 -3 31
• Question 3

Work out the value of the following expression when a = 10 and b = -3

20 + 2a - b

43
EDDIE SAYS
20 + 2a - b 20 + (2 x a) - b 20 + (2 x 10) - (-3) 20 + 20 + 3 43
• Question 4

Work out the value of the following expression when a = 10 and b = 0

5a + a + 42b

60
EDDIE SAYS
5a + a + 42b (5 x a) + a + (42 x b) (5 x 10) + 10 + (42 x 0) 50 + 10 + 0 60
• Question 5

Work out the value of the following expression when a = 10 and b = 4

3b + 5a + 2 + a

74
EDDIE SAYS
3b + 5a + 2 + a (3 x b) + (5 x a) + 2 + a (3 x 4) + (5 x 10) + 2 + 10 12 + 50 + 2 + 10 74
• Question 6

Work out the value of the following expression when a = 8 and b = -3

b + 24 - 2a

5
EDDIE SAYS
b + 24 - 2a b + 24 - (2 x a) -3 + 24 - (2 x 8) -3 + 24 - 16 5
• Question 7

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

10 - 2a - b

6
EDDIE SAYS
10 - 2a - b 10 - (2 x a) - b 10 - (2 x 4) - (-4) 10 - 8 + 4 6
• Question 8

Work out the value of the following expression when a = 4 and b = 2

2a + 5 - 3b

7
EDDIE SAYS
2a + 5 - 3b (2 x a) + 5 - (3 x b) (2 x 4) + 5 - (3 x 2) 8 + 5 - 6 7
• Question 9

Work out the value of the following expression when a = 7 and b = -2

2a + 6 + 5b

10
EDDIE SAYS
2a + 6 + 5b (2 x a) + 6 + (5 x b) (2 x 7) + 6 + (5 x -2) 14 + 6 - 10 10
• Question 10

Work out the value of the following expression when a = 4 and b = -2

2a - 7 - 3b

7
EDDIE SAYS
2a - 7 - 3b (2 x a) - 7 - (3 x b) (2 x 4) - 7 - (3 x -2) (8) - 7 - (-6) 8 - 7 + 6 7
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