EARLY OPERATIONS · TEXTBOOK LESSON
Subtraction can represent taking away, finding the difference between two quantities, or finding a missing part. Understanding these meanings helps you choose the best strategy.
Learning objectives
By the end of this lesson, you should be able to:
- Interpret subtraction as take-away, difference and missing-part problems.
- Subtract mentally using counting back, counting up or partitioning.
- Use column subtraction accurately, including regrouping.
- Check subtraction using addition.
1. Key vocabulary and definition
Definition
For a - b = c, a is the starting quantity, b is the amount subtracted and c is the difference. Addition and subtraction are inverse operations.
minuendsubtrahenddifferenceinverseregroup
2. Essential facts and rules
These are the facts you should know before attempting the worked example.
Key mathematical facts
- Subtracting zero leaves a number unchanged.
- Subtracting a number from itself gives zero.
- Counting up is often efficient when two numbers are close together.
3. Standard method
A reliable method helps prevent errors and makes your reasoning easy to follow.
1
Identify the starting amount and the amount being removed or compared.
2
Choose counting back, counting up, partitioning or column subtraction.
3
Keep place values aligned in a written method.
4
Regroup one unit from the next place value when necessary.
5
Check by adding the difference to the number subtracted.
4. Worked example
Worked example
Calculate 52 - 28.
1
Count up from 28 to 30: +2.
2
Count from 30 to 50: +20.
3
Count from 50 to 52: +2.
4
Total increase = 2 + 20 + 2 = 24, so 52 - 28 = 24. Check: 28 + 24 = 52.
5. Common mistakes
Watch out for these
- Starting calculations before deciding what the question is asking.
- Skipping important steps or changing notation midway through a solution.
- Accepting an answer without checking whether its size, sign or unit is sensible.
6. Video lesson
This topic is ready for a matching video lesson. The written textbook lesson is fully available now; additional videos can be added to the same lesson template.
7. Practice exercise
Complete these without looking at the answers first.
- Calculate 15 - 7.
- Calculate 40 - 18.
- Calculate 73 - 46.
- Find the missing number: □ - 19 = 25.
- A shop had 65 notebooks and sold 27. How many remain?
Show answers
- 8
- 22
- 27
- 44
- 38 notebooks
8. Chapter summary
- Understand the underlying idea before memorising a procedure.
- Use precise mathematical notation and show a logical method.
- Always check the final result.