Primary 2 · Mathematics

P2 addition and subtraction within 1000

A P2 two-step word problem can end with a sum that is correct and still not the answer. One bracket on the model shows what the question really asked for.

Level
P2
Usually taught
Term 1
Covers
2 concepts

What changes at P2

In Primary 2, addition and subtraction go up to 1000. Your child adds and subtracts 3-digit numbers with the column method, regrouping when a column reaches ten, and works out easier ones like 245 + 80 in their head.

Word problems (problem sums, as most parents know them) gain a second step, and P2 is where the model arrives in written working: bars drawn from a common starting line, with a bracket for what the question asks. The step (a) and step (b) labels start here too.

The sentence that costs the mark

Mei has 245 stickers. Jun has 80 fewer than Mei. How many stickers do they have altogether?

What the working usually does

the answer:Jun's stickers=165

Works out Jun's stickers and stops there.

What the question asked

the answer:both together=410

Uses Jun's 165 as step (a), then adds both.

245 − 80 = 165 is correct, neatly written, and it uses every number in the question, so it looks finished. The question just asked about both children.

Jun has 80 fewer than Mei. How many altogether?

The same question, worked properly

  1. Step (a): Jun's stickers

    245 − 80 = 165

    Jun has 80 fewer than Mei, so take 80 from 245. On the model, this is Jun's bar, the shorter one.

  2. Read the question again

    altogether = Mei + Jun

    This is the step that fails. It asks for both children's stickers, so 165 is only Jun's share. A first sum that comes out cleanly is easy to mistake for the answer.

  3. Step (b): altogether

    245 + 165 = 410

    They have 410 stickers altogether. Writing that answer sentence is what catches a step (a) answer.

How can you tell it has clicked?

Cover the last sentence of a two-step problem and ask what your child would work out first. Then uncover it and ask whether that number is the answer.

A child who says "no, that is only Jun's, I still need both" has it. A child who says yes has found a real number and matched it to the wrong question, which is the slip on this page.

One thing to try tonight

Before your child writes any sum, ask them to point at the part of the model the question is asking about.

If the finger lands on Jun's bar, ask them to read the last sentence of the question aloud, then point again. Ten seconds, and it targets exactly the step that fails.

What your child will meet in this topic

  • Adding Within 1000
  • Subtracting Within 1000

Most Singapore schools introduce this in Term 1, though schools do differ by a term either way. If your child’s school runs a different order, you can set it in the schedule on your dashboard.

What it leads to

In P3 the column method reaches 10 000, including regrouping across zeros, as in 5003 − 1568.

The model keeps growing. By P5 and P6 the same bars carry fractions and ratio, and the first question is still which bracket the problem is asking about.

The same topic in other years

It comes back each year and gets harder, so it helps to see what came before and what is coming.

More in Primary 2

Other topics in the same year, so you can see what sits either side of this one.

Struggling with the working rather than the topic itself? How to help your child with problem sums

See how your child is doing on this topic

StudyLah marks each step separately, so you can see whether it was the setup or the arithmetic that cost the mark.

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