Substitution
The Maths Habit
In football, what does a substitute do?
A new player comes on in place of another. In maths, a number takes the place of a letter.
What does 3a mean?
Work out
- Expression
- Letters, numbers and signs, with no equals sign.
- Substitute
- Swap a letter for its number.
- Formula
- A rule with an equals sign that works out one thing from others.
3a means 3 × a
3 × 5 = 15, not 35
Work out 3a + 2
when a = 5
Work out 2a + 7
when a = 4
Work out 5b + 1
when b = 3
Work out 2a + 7
when a = 4
Work out 4c − 3
when c = 5
Work out 2a + 7
when a = 4
Work out 3d + 10
when d = 6
Work out 2a + 7
when a = 4
Work out 10m − 4
when m = 2
Work out 2n + 9
when n = 5
Work out 5t − 6
when t = 4
Work out 3k + 4
when k = 7
2a + 4b
when a = 3 and b = 5
Which number takes the place of b? 5
Work out 3a + 2b
when a = 5 and b = 4
Work out 2m + 4n
when m = 6 and n = 3
Work out 3a + 2b
when a = 5 and b = 4
Work out 5p − 2q
when p = 4 and q = 3
Work out 3a + 2b
when a = 5 and b = 4
Work out 4r + 3s
when r = 2 and s = 5
Work out 3a + 2b
when a = 5 and b = 4
Work out 10c − 3d
when c = 3 and d = 4
Work out 4k + 2m
when k = 5 and m = 6
Work out 3s − 2t
when s = 6 and t = 4
Work out 5w + 3y
when w = 2 and y = 7
Answer sheet
Is the swap right? Thumbs up: yes. Thumbs down: no.
4a + 1 when a = 6 4 × 6 + 1
Yes2b + 5 when b = 7 27 + 5
No: 2 × 7 + 55c − 3 when c = 2 5 × 2 − 3
Yes3m + 2n when m = 4 and n = 1 3 × 1 + 2 × 4
No: 3 × 4 + 2 × 110k + 5 when k = 3 103 + 5
No: 10 × 3 + 5
4n + □ = 27 when n = 5. What is □?
7p = 2 and q = 6. Which is bigger: 5p or 2q?
2q (12 is bigger than 10)a = 3. Write an expression in a that is worth 20.
For example 6a + 2a² means a × a. Work out a² + 1 when a = 4.
17
Work out 5a + 3 when a = 4. The swap is given: 5 × 4 + 3
23Work out 3m − 2n when m = 8 and n = 5
14Work out 4b + 7 when b = 6. Show your steps.
31