Websink Prep UKKS1 MathsYear 2 chaptersMaths textbooksYear 1Year 2Year 4Year 5Year 6GCSEBrowse allPast papersFind a tutorBecome a tutor
Primary Maths · Year 2Chapter 2 · Adding and subtracting
Year 2 · Adding and subtracting · Lesson 2.5

Year 2: Adding three numbers and the order of numbers

Part of the Year 2 adding and subtracting chapter. Chapter overview · whole chapter on one page

2.5

Adding three numbers and the order of numbers

Year 2
Add three one-digit numbers, Show that addition can be done in any order and subtraction cannot
Three groups of things in the park.

We can add three one-digit numbers. Look for two numbers that make 10 first.

For 4 + 6 + 3: 4 + 6 = 10. Then 10 + 3 = 13.

Adding works in any order: 5 + 2 is the same as 2 + 5. Taking away does not.

Three groups of stars: 4, 6 and 3.

Key ideas

  • Look for two numbers that make 10 first.
  • Then add the last number.
  • Adding can be done in any order.
  • Taking away cannot be done in any order.
Worked example 2.5.1
Work out 4 + 6 + 3.

Method. Find two numbers that make 10 first. Then add the last number.

  1. Look for two numbers that make 10. 4 and 6 make 10.
    4 + 6 = 10
  2. Add the last number. Then add the number that is left.
    10 + 3 = 13
  3. Write the answer.
    13

Check. Add them in a different order to check: 3 + 6 + 4 = 13. ✓

Watch out. Keep the numbers in your head. Do not forget the last number.

Worked example 2.5.2
Work out 3 + 6 + 8. No two of them make 10, so add two first.

Method. Add two numbers first. Then add the last number.

  1. Add the first two numbers. Start with the first two numbers.
    3 + 6 = 9
  2. Add the last number. Add 8 to the answer so far.
    9 + 8 = 17
  3. Write the answer.
    17

Check. Add them in a different order to check: 8 + 6 + 3 = 17. ✓

Watch out. Keep the numbers in your head. Do not forget the last number.

Worked example 2.5.3
Is 5 + 2 the same as 2 + 5?

Method. Swap the two numbers. Check that the answer is the same.

  1. Add the numbers in one order. 5 and 2 make 7.
    5 + 2 = 7
  2. Swap the numbers and add again. Now the bigger number comes first.
    2 + 5 = 7
  3. Compare the answers. Both answers are the same, so the order does not matter.
    Yes. 5 + 2 = 2 + 5

Check. Both orders make 7. ✓

Watch out. Adding is in any order. Taking away is NOT in any order.

Watch out

Watch out: 9 − 4 is 5. But 4 − 9 cannot be done. Taking away is not in any order.

Exam tip

Grown-up tip. Use three cups of pasta. Ask: “Which two cups make 10?” Then ask: “Does it matter which one we add first?”

Exercise 2E  Adding three numbers and the order of numbers

Non-calculator
1
FWork out 2 + 5 + 3.
2
FWork out 6 + 3 + 4.
3
FWork out 7 + 1 + 9.
4
FWork out 5 + 8 + 5.
5
FWork out 3 + 6 + 8.
6
FWork out each sum.
(a)4 + 3 + 6
(b)9 + 2 + 8
(c)5 + 5 + 4
7
PSAmira has 4 red pens, 5 blue pens and 6 green pens. How many pens does she have?
8
PSThree bags have 3, 7 and 8 sweets. How many sweets are there altogether?
9
RIs 8 + 6 the same as 6 + 8? Explain how you know.
10
RPriya says 9 − 4 is the same as 4 − 9. Is she right? Explain.
11
RWhich one can we NOT work out with objects: 7 − 3 or 3 − 7?

Websink Prep UK is an independent site. It is not affiliated with, endorsed by or sponsored by AQA, Pearson Edexcel, OCR, WJEC, Eduqas, CCEA, SQA, GL Assessment, CEM or the Department for Education. All exam board names and trademarks belong to their owners. Past papers are linked from the exam boards' own websites and are not hosted here.

About Websink Prep UK · Find a tutor · Privacy · Terms · Cookie settings