Addition & Subtraction within 20
This topic covers 3 learning steps, guiding your child from the basics through to confident problem-solving. Each step includes a worked example and adaptive practice questions.
What Your Child Will Learn
- Add within 20
Add two numbers within 20 - Subtract within 20
Subtract within 20 - Mixed Problems
Mixed add and subtract
Common Mistakes
- Not understanding place value when adding two-digit numbers (e.g. adding 23+14 as 2+1 and 3+4 without understanding tens and units)
Use base-10 blocks: 23 is 2 sticks of ten and 3 ones. Adding 14 (1 ten and 4 ones) makes 3 tens and 7 ones = 37. Physical manipulatives make place value visible. - Forgetting to "exchange" when addition goes over 10 in the units column (e.g. 28+15 — writing 13 in the units and not carrying the ten)
When the units add to more than 9, we exchange 10 ones for 1 ten. Practise with counters: "We have 13 ones — that's too many for the ones column. We swap 10 ones for 1 ten."
Tips for Parents
- Use real money to practise: adding two amounts together makes abstract addition concrete. "You have 34p and I give you 27p — how much now?"
- Draw a blank number line. Start at one number, jump in tens, then jump in ones. This partitioning strategy is powerful for mental maths.
- Play "Target 50" with two dice — keep a running total and try to reach exactly 50. This builds mental addition stamina.
- When checking homework, ask your child to EXPLAIN their method, not just give the answer. Understanding the method matters more than the result.
Key Words
- Tens — The place value column for groups of 10 — in 35, the 3 means 3 tens (30).
- Units (ones) — The place value column for single numbers — in 35, the 5 means 5 ones.
- Exchange — Swap 10 ones for 1 ten (or the other way round) when adding or subtracting.
- Column method — Writing numbers in columns (tens and units) to add or subtract systematically.
- Place value — The value of a digit depending on its position — the 3 in 30 is worth 30, but the 3 in 300 is worth 300.
Where This Fits
Before this topic: Children should add and subtract confidently within 20 and understand that 10 ones = 1 ten.
After this topic: Addition and subtraction within 100 leads to working with hundreds in Year 3 and formal column methods.
How MathCraft Teaches This
In MathCraft, Addition & Subtraction within 20 is taught through the Geometry & Shape adventure track. Your child follows guided lessons with friendly characters, works through examples step by step, then practises with questions that adapt to their level.
The adaptive engine tracks mastery across all 3 steps, revisiting concepts your child finds tricky and advancing when they're ready. Parents can see detailed progress in the Parent Dashboard.
Practise Addition & Subtraction within 20 with MathCraft
Step-by-step lessons, worked examples, and adaptive practice — all wrapped in an adventure game your child will love.
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