 # Substitute Numbers for Letters into an Expression

In this worksheet, students must substitute numbers in place of letters to evaluate the given expressions. Key stage:  KS 2

Curriculum topic:  Maths and Numerical Reasoning

Curriculum subtopic:  Equations and Algebra

Difficulty level:   ### QUESTION 1 of 10

In algebra, we use a letter to represent an unknown number.

Sometimes we want to substitute a number for the letter in an expression.

Example 1

Evaluate 2a - b when a = 6 and b = 7.

2a - b means (2 × a) - b

So this is (2 × 6) - 7

i.e.  12 - 7 = 5.

Example 2

Work out the value of 5(x - 2) when x = 9.

Substitute x for 9 to get

5(9 - 2) which means 5 × (9 - 2).

Now work out the brackets first to get 9 - 2 = 7.

So this is 5 × 7 = 35

Work out the value of

2x + y   when  x = 6 and  y = 7

Work out the value of

2x + y   when  x = 5 and  y = 4

Evaluate

2x + y   when  x = 10 and  y = 9

Evaluate

2x - y   when  x = 10 and  y = 9

Evaluate

2(x - 5)   when  x = 10

Evaluate

12(x - 6)    when  x = 9

Evaluate

9(x + 6)   when  x = 5

Evaluate

2(x + y)   when  x = 10 and  y = 9

Evaluate

2(x + y)   when  x = 1 and  y = 19

Work out the value of

5x - y    when  x = 2 and  y = 10

• Question 1

Work out the value of

2x + y   when  x = 6 and  y = 7

19
EDDIE SAYS

Step 1: Rewrite the expression with the hidden multiply signs

2 x X + y

Step 2: Substitute in the numbers you are given

2 x 6 + 7

Step 3: Evaluate the expression (don't forget to use BODMAS)

12 + 7 = 19

• Question 2

Work out the value of

2x + y   when  x = 5 and  y = 4

14
EDDIE SAYS

Step 1: Rewrite the expression with the hidden multiply signs

2 x X + y

Step 2: Substitute in the numbers you are given

2 x 5 + 4

Step 3: Evaluate the expression (don't forget to use BODMAS)

10 + 4 = 14

• Question 3

Evaluate

2x + y   when  x = 10 and  y = 9

29
EDDIE SAYS

Step 1: Rewrite the expression with the hidden multiply signs

2 x X + y

Step 2: Substitute in the numbers you are given

2 x 10 + 9

Step 3: Evaluate the expression (don't forget to use BODMAS)

20 + 9 = 29

• Question 4

Evaluate

2x - y   when  x = 10 and  y = 9

11
EDDIE SAYS

Step 1: Rewrite the expression with the hidden multiply signs

2 x X - y

Step 2: Substitute in the numbers you are given

2 x 10 - 9

Step 3: Evaluate the expression (don't forget to use BODMAS)

20 - 9 = 11

• Question 5

Evaluate

2(x - 5)   when  x = 10

10
EDDIE SAYS

Step 1: Substitute in the numbers you are given

2(10 - 5)

Step 2: Evaluate the expression (don't forget to use BODMAS)

2 x 5 = 10

• Question 6

Evaluate

12(x - 6)    when  x = 9

36
EDDIE SAYS

Step 1: Substitute in the numbers you are given

12(9 - 6)

Step 2: Evaluate the expression (don't forget to use BODMAS)

12 x 3 = 36

• Question 7

Evaluate

9(x + 6)   when  x = 5

99
EDDIE SAYS

Step 1: Substitute in the numbers you are given

9(5 + 6)

Step 2: Evaluate the expression (don't forget to use BODMAS)

9 x 11 = 99

• Question 8

Evaluate

2(x + y)   when  x = 10 and  y = 9

38
EDDIE SAYS

Step 1: Substitute in the numbers you are given

2(10 + 9)

Step 2: Evaluate the expression (don't forget to use BODMAS)

2 x 19 = 38

• Question 9

Evaluate

2(x + y)   when  x = 1 and  y = 19

40
EDDIE SAYS

Step 1: Substitute in the numbers you are given

2(1 + 19)

Step 2: Evaluate the expression (don't forget to use BODMAS)

2 x 20 = 40

• Question 10

Work out the value of

5x - y    when  x = 2 and  y = 10

0
EDDIE SAYS

Step 1: Rewrite the expression with the hidden multiply signs

5 x X - y

Step 2: Substitute in the numbers you are given

5 x 2 - 10

Step 3: Evaluate the expression (don't forget to use BODMAS)

10 - 10 = 0

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