Substitute a value
If p = 4, then p + 7 = 11.
Replace the letter with the value.
Year 6
Use simple formulae
Substitute numbers into a simple formula and work out the answer.
Lesson overview
Algebra
A formula uses letters to stand for numbers. When a value is given, we substitute it into the formula and calculate carefully.
Use more than one value
If n = 6, then 2n = 12.
2n means 2 multiplied by n.
Worked example
If a = 5, work out 3a + 2.
| a | 3a | 3a + 2 |
|---|---|---|
| 5 | 15 | 17 |
- Substitute 5 for a.
- 3a means 3 x 5 = 15.
- Add 2.
- So 3a + 2 = 17.
Try it
Replace the letter first, then calculate the expression carefully.
Question 1
If p = 4, then p + 7 =
Question 2
If n = 6, then 2n =
Question 3
If a = 5, then 3a + 2 =
Question 4
If x = 9, then x - 4 =
Question 5
Which expression means double y?
2 x y
2y
Common mistakes
Watch for these when working through the lesson.
- Treating 2n as 2 + n instead of 2 x n.
- Forgetting to substitute the value of the letter.
- Doing the operations in the wrong order.
Related topics
These ideas fit closely with this lesson.
- Generate and describe linear number sequences.
- Express missing number problems algebraically.