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Primary 3 · Mathematics · Number

Adding and subtracting larger numbers

Using place value, jump strategies on a number line and partitioning to add and subtract two- and three-digit numbers, and checking answers with the inverse operation.

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. How we review

These lessons were written around Australian Curriculum strands and matched to Singapore levels by age (Primary 1 is the first year of primary school). They are not aligned to MOE syllabuses or the PSLE, so check them against the syllabus your child is working towards.

Learning goals

Learners will

  • Add and subtract two- and three-digit numbers by partitioning into hundreds, tens and ones.
  • Use jumps on an empty number line to add and subtract.
  • Check answers using the inverse operation.

Success looks like

  • I can split numbers into hundreds, tens and ones to add them.
  • I can draw jumps on a number line to add or subtract.
  • I can check a subtraction with an addition, and an addition with a subtraction.

The big idea

In Primary 3, children add and subtract bigger numbers by using what they know about place value. Instead of counting by ones, they work with hundreds, tens and ones.

Partitioning means splitting numbers into parts. To add 245 + 132, split both: 200 + 100 = 300, 40 + 30 = 70 and 5 + 2 = 7. Then put the parts back together: 300 + 70 + 7 = 377.

Sometimes the ones add up to 10 or more. For 48 + 36: 40 + 30 = 70 and 8 + 6 = 14. Then 70 + 14 = 84. The 14 ones become 1 more ten and 4 ones.

An empty number line is a great way to show thinking. For 63 + 28, start at 63, jump 20 to 83, then jump 8 to 91. Some children prefer to jump to a friendly ten: 63 + 7 = 70, then 70 + 21 = 91. Both are correct.

Subtraction can be shown as jumping back. For 352 − 127, start at 352, jump back 100 to 252, back 20 to 232, then back 7 to 225. Another way is to find the difference by jumping forwards from 127 to 352.

Addition and subtraction undo each other, so they are inverse operations. To check 352 − 127 = 225, add 225 + 127. If you get 352, the answer is right. To check an addition, subtract one part from the total.

Before calculating, make a quick estimate. 352 − 127 is about 350 − 130 = 220, so 225 is sensible. If you got 479, the estimate would warn you something went wrong.

  • Partition: 245 + 132 = 300 + 70 + 7 = 377.
  • Jump: 63 + 20 = 83, then 83 + 8 = 91.
  • Check: 225 + 127 = 352, so 352 − 127 = 225 is correct.

Worked examples

Adding by partitioning

What is 245 + 132?

  1. Split both numbers: 245 = 200 + 40 + 5 and 132 = 100 + 30 + 2.
  2. Add the hundreds: 200 + 100 = 300.
  3. Add the tens: 40 + 30 = 70.
  4. Add the ones: 5 + 2 = 7.
  5. Put them together: 300 + 70 + 7 = 377.

Answer: 245 + 132 = 377.

Adding with jumps on a number line

What is 63 + 28?

  1. Draw an empty number line and mark 63 at the start.
  2. Jump forwards 20 to land on 83.
  3. Jump forwards 8 more to land on 91.
  4. Estimate check: 60 + 30 = 90, so 91 is sensible.

Answer: 63 + 28 = 91.

Subtracting and checking with the inverse

What is 352 − 127? Check your answer.

  1. Start at 352 and jump back 100 to 252.
  2. Jump back 20 to 232.
  3. Jump back 7 to 225.
  4. Check with addition: 225 + 127 = 200 + 100 + 20 + 20 + 5 + 7 = 352. It matches.

Answer: 352 − 127 = 225.

Practice check

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

  1. 1.What is 34 + 25?
  2. 2.What is 156 + 230?
  3. 3.What is 82 − 37?
  4. 4.Which addition checks that 145 − 62 = 83?
  5. 5.What is 48 + 36?
  6. 6.A library has 425 books. 140 books are borrowed. How many books are still on the shelves?
  7. 7.Which jumps on a number line correctly work out 67 + 25?
  8. 8.A family drives 268 km on Saturday and 315 km on Sunday. How far do they drive altogether?
Answer guide for parents

  1. What is 34 + 25?

    59 — 30 + 20 = 50 and 4 + 5 = 9, so 50 + 9 = 59.

  2. What is 156 + 230?

    386 — 100 + 200 = 300, 50 + 30 = 80, 6 + 0 = 6. So 300 + 80 + 6 = 386.

  3. What is 82 − 37?

    45 — Jump back 30 from 82 to 52, then back 7 to 45. Check: 45 + 37 = 82.

  4. Which addition checks that 145 − 62 = 83?

    83 + 62 = 145 — Adding the answer back to the number taken away should give the starting number: 83 + 62 = 145.

  5. What is 48 + 36?

    84 — 40 + 30 = 70 and 8 + 6 = 14. Then 70 + 14 = 84.

  6. A library has 425 books. 140 books are borrowed. How many books are still on the shelves?

    285 — 425 − 100 = 325, then 325 − 40 = 285. Check: 285 + 140 = 425.

  7. Which jumps on a number line correctly work out 67 + 25?

    67 + 20 = 87, then 87 + 5 = 92 — Jump 20 from 67 to 87, then 5 more to 92. So 67 + 25 = 92.

  8. A family drives 268 km on Saturday and 315 km on Sunday. How far do they drive altogether?

    583 km — 200 + 300 = 500, 60 + 10 = 70, 8 + 5 = 13. Then 500 + 70 + 13 = 583 km.

Watch out for

  • Writing the tens and ones side by side instead of regrouping (48 + 36 written as 714). Show that 14 ones is 1 ten and 4 ones using bundles of sticks.
  • Subtracting the smaller digit from the larger in each place (82 − 37 answered as 55). Use jumps on a number line to show the real difference.
  • Skipping the check. Make 'estimate first, check with the inverse after' a routine for every question.

Tips for parents

  • Ask your child to talk you through their number line jumps — explaining strategies builds understanding.
  • Accept different strategies; the best strategy is the one your child understands and can use accurately.
  • Use real contexts: adding prices on a shopping list or working out how many pages are left in a book.

Go further

  • Plan a pretend shopping trip with a $500 budget and add up items, then work out the change.
  • Roll three dice to make two 3-digit numbers, add them, and check the answer with subtraction.
  • Find the difference between the page numbers of two places in a long book, using a number line.

About 40 minutes

Make a lesson planAssign to my child

You'll need

  • Paper and pencil for number lines
  • Place value blocks, or bundles of 10 pop sticks and single sticks
  • Play money in $100, $10 and $1 amounts (optional)
  • A calculator for checking at the end (optional)

Key words

partition
Split a number into parts, such as 245 = 200 + 40 + 5.
place value
The value of a digit depends on its place: hundreds, tens or ones.
number line
A line used to show numbers in order and jumps between them.
difference
How much bigger one number is than another; the answer to a subtraction.
inverse operation
The opposite operation that undoes another; addition and subtraction are inverses.
estimate
A sensible, rounded guess used to check whether an answer is reasonable.
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