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Year 2 · Mathematics · Number

Adding and subtracting within 20

Solving simple addition and subtraction stories within 20 using objects, counting on, counting back, doubles and fact families.

Awaiting educator review. This material was drafted by our content team with AI assistance and is waiting for review by a qualified educator. Please check it suits your child before using it. Created 10 October 2026.

These lessons were written around Australian Curriculum strands and matched to New Zealand year levels by age (NZ Year 1 is the first year of school). They are not yet mapped to The New Zealand Curriculum, so check them against your own learning programme.

Learning goals

Learners will

  • Solve addition and subtraction stories within 20 using objects and drawings.
  • Use counting on and counting back from the larger number.
  • Notice that addition and subtraction facts are related.

Success looks like

  • I can count on from the bigger number to add.
  • I can count back to take away.
  • I can use a fact I know, like 5 + 5 = 10, to help me.
  • I can write a number sentence for a story.

The big idea

Children first add by counting every object. The next step is to count on: keep the bigger number in your head and count on the smaller number. For 8 + 5, say 'eight' and then count on five more: 9, 10, 11, 12, 13.

It is quicker to start with the bigger number. 2 + 9 gives the same answer as 9 + 2, but counting on 2 from 9 is much easier than counting on 9 from 2.

For subtraction, count back. For 15 − 3, start at 15 and count back three: 14, 13, 12. A paper number strip helps your child see the jumps.

Doubles are worth learning by heart: 1 + 1, 2 + 2, all the way to 10 + 10. They help with near-doubles too: if 6 + 6 = 12, then 6 + 7 is one more, 13.

Making ten is another powerful idea. Fill an egg carton of 10. For 9 + 4, move 1 of the 4 into the empty cup to make 10, leaving 3. Then 10 + 3 = 13.

Addition and subtraction are linked. The numbers 4, 9 and 13 make a fact family: 4 + 9 = 13, 9 + 4 = 13, 13 − 9 = 4 and 13 − 4 = 9.

Worked examples

Counting on

Ella has 11 shells. She finds 4 more. How many shells does she have now?

  1. The bigger number is 11, so start there.
  2. Count on four: 12, 13, 14, 15.
  3. Write the number sentence: 11 + 4 = 15.

Answer: Ella has 15 shells.

Making ten

What is 8 + 5?

  1. Fill 8 cups of a 10-cup egg carton.
  2. Two more cups need filling to make 10, so take 2 from the 5. That leaves 3.
  3. 10 + 3 = 13.

Answer: 8 + 5 = 13.

Counting back

There are 14 biscuits. 6 are eaten. How many are left?

  1. Start at 14.
  2. Count back six: 13, 12, 11, 10, 9, 8.
  3. Write the number sentence: 14 − 6 = 8.

Answer: 8 biscuits are left.

Practice check

Have a go, then check your answers. Each answer comes with an explanation.

  1. 1.What is 8 + 5?
  2. 2.What is double 6? (6 + 6)
  3. 3.What is 15 − 3?
  4. 4.What is 7 + 3?
  5. 5.Noah has 11 marbles and wins 4 more. How many marbles does he have now?
  6. 6.There are 16 biscuits on a plate. 7 are eaten. How many biscuits are left?
  7. 7.Which fact is in the same fact family as 4 + 9 = 13?
  8. 8.Sam has 17 stickers and Ava has 12 stickers. How many more stickers does Sam have than Ava?
Answer guide for parents

  1. What is 8 + 5?

    13 — Start at 8 and count on 5: 9, 10, 11, 12, 13.

  2. What is double 6? (6 + 6)

    12 — 6 + 6 = 12. This is a doubles fact.

  3. What is 15 − 3?

    12 — Start at 15 and count back 3: 14, 13, 12.

  4. What is 7 + 3?

    10 — 7 and 3 make 10. Count on from 7: 8, 9, 10.

  5. Noah has 11 marbles and wins 4 more. How many marbles does he have now?

    15 — Start at 11 and count on 4: 12, 13, 14, 15.

  6. There are 16 biscuits on a plate. 7 are eaten. How many biscuits are left?

    9 — 16 − 7 = 9. Count back 7 from 16: 15, 14, 13, 12, 11, 10, 9.

  7. Which fact is in the same fact family as 4 + 9 = 13?

    13 − 9 = 4 — The fact family uses 4, 9 and 13: 4 + 9 = 13, 9 + 4 = 13, 13 − 9 = 4 and 13 − 4 = 9.

  8. Sam has 17 stickers and Ava has 12 stickers. How many more stickers does Sam have than Ava?

    5 — Count on from 12 to 17: 13, 14, 15, 16, 17. That is 5 more.

Watch out for

  • Including the starting number when counting on (saying '8, 9, 10, 11, 12' for 8 + 5). Remind your child that the first count is the next number after the start.
  • Always starting with the first number even when it is smaller. Show that 2 + 9 and 9 + 2 give the same answer, so start with the bigger one.
  • Thinking subtraction can be done in any order, like addition. Use objects to show that 6 − 2 is not the same as 2 − 6.

Tips for parents

  • Turn sums into short stories about your family, pets or favourite foods.
  • Practise doubles in the car or at the shops — 'What is double 7?'
  • Let your child use fingers or objects for as long as they need; speed comes with practice.

Go further

  • Play 'Snap to 10': deal number cards 1 to 9 and find pairs that make 10.
  • Roll two dice and add the numbers. Record which totals come up most often.
  • Create fact family 'houses': draw a roof with three numbers and write the four facts inside.