# Substitution (2)

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

Key stage:  KS 2

Curriculum topic:   Maths and Numerical Reasoning

Curriculum subtopic:   Equations and Algebra

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 = -4 and b = 3

2a + 5 + 2b

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

2a + 6 - b

Work out the value of the following expression when a = -9 and b = -2

2a - 7 - b

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

a + a + 2b

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

5a + 2 - 5b

Work out the value of the following expression when a = -8 and b = 0

2 - 2a - 54b

Work out the value of the following expression when a = -4 and b = 9

10 - 2a - 2b

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

20 - a - b

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

20 + 2a - 2b

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

20 + 2a - 2b

• Question 1

Work out the value of the following expression when a = -4 and b = 3

2a + 5 + 2b

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

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

2a + 6 - b

-11
EDDIE SAYS
2a + 6 - b (2 x a) + 6 - b (2 x -7) + 6 - 3 -14 + 6 - 3 -11
• Question 3

Work out the value of the following expression when a = -9 and b = -2

2a - 7 - b

-23
EDDIE SAYS
2a - 7 - b (2 x a) - 7 - b (2 x -9) - 7 - -2 -18 - 7 + 2 -23
• Question 4

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

a + a + 2b

-14
EDDIE SAYS
a + a + 2b a + a + (2 x b) (-10) + (-10) + (2 x 3) -10 -10 + 6 -14
• Question 5

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

5a + 2 - 5b

2
EDDIE SAYS
5a + 2 - 5b (5 x a) + 2 - (5 x b) (5 x -3) + 2 - (5 x -3) (-15) + 2 - (-15) -15 + 2 + 15 2
• Question 6

Work out the value of the following expression when a = -8 and b = 0

2 - 2a - 54b

18
EDDIE SAYS
2 - 2a - 54b 2 - (2 x a) - (54 x b) 2 - (2 x -8) - (54 x 0) 2 - (-16) - (0) 2 + 16 + 0 18
• Question 7

Work out the value of the following expression when a = -4 and b = 9

10 - 2a - 2b

0
EDDIE SAYS
10 - 2a - 2b 10 - (2 x a) - (2 x b) 10 - (2 x -4) - (2 x 9) 10 - (-8) - (18) 10 + 8 - 18 0
• Question 8

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

20 - a - b

24
EDDIE SAYS
20 - a - b 20 -(-7) - (3) 20 + 7 - 3 24
• Question 9

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

20 + 2a - 2b

-8
EDDIE SAYS
20 + 2a - 2b 20 + (2 x a) - (2 x b) 20 + (2 x -7) - (2 x 7) 20 + (-14) - (14) 20 - 14 - 14 -8
• Question 10

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

20 + 2a - 2b

8
EDDIE SAYS
20 + 2a - 2b 20 + (2 x a) - (2 x b) 20 + (2 x -10) - (2 x -4) 20 + (-20) - (-8) 20 - 20 + 8 8
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