Mathematics

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50 mins

Teacher/Student led

Learning Goals

Learning Outcomes

Lesson Files

+80 XP

Teacher-led from the board. Pupils do not need a device, but can follow on one.

What you need:
IWB/Projector/Large Screen

Using a Letter or Word for the Unknown

You'll learn to use a letter to stand for a missing number in a number sentence, then find its value by keeping both sides of the balance equal. You'll check your answer by putting the number back in and reading the sentence.

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1 Getting Started
2 Watch and Notice
3 Try It Together
4 Find the Letters in Your Copy
5 Class Challenge
6 What Did We Notice?
7 What's Next
Pupil practice

Your turn

Your teacher is running this lesson on the board. Here is the part you can try yourself.

Your written work is on page 113

Balance scales

1 - Getting Started ~4 mins

A level balance with a + 3 on the left pan and 10 on the right pan

Key point

Here is a puzzle on a balance: a + 3 = 10. The letter a is hiding a number. Both pans have to weigh the same, so the beam stays level. What number do you think a is hiding?

👇 Mark your steps as done as you complete them.

+5 XP

2 - Watch and Notice ~9 mins

Watch these balanced sentences on the scales. In each one a letter is standing in for a missing number. Work out each letter's number before it is shown, then check that it keeps both pans level. The letter is just a name for that number.

In the next one the total is on the left — the balancing job is still the same.

In the last one the same letter appears twice. That means two of the same hidden number added together.

👇 Mark your steps as done as you complete them.

+10 XP

3 - Try It Together ~9 mins

Key point

Each time we say the value of the letter aloud. Then we read the whole sentence back with the number in place of the letter to check both sides match.

Let us find the value of the letter together. First we work e + 4 = 9 on the balance, sliding the letter block until the beam is level. Then we work three more the same way at the board: g − 3 = 8, then 7 + h = 16, then 13 = k + 5.

Find the value of the letter

+15 XP

4 - Find the Letters in Your Copy ~3 mins

COPYBOOK MOMENT

In your maths copy, find the value of the letter in each of these, then write the full sentence with the number in place of the letter:

a + 5 = 12
n − 4 = 6
9 = m + 2

Read each finished sentence back to yourself to check both sides match.

+10 XP

Pupil practice

Module 10 · Algebra: Patterns, Rules and Number Sentences Algebra

Lesson 122 · Using a Letter or Word for the Unknown

Download Activity Book page (PDF)

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