Module 3 Knowing and using number facts
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Can I recall all pairs of numbers that total 20?

Example review questions

  • What addition sentences could you write to match the beads on this bead string?
    A bead string with 4 white beads and 17 yellow beads
  • What is 20 subtract 15?
  • empty box + empty box = 20 What could the missing numbers be?
  • If you know 17 + 3 = 20, what is 20 − 17 and 20 − 3?
  • If there are 20 counters altogether, how many are hidden in the pot? What subtraction sentence could you write to show this?
    A pot with 16 counters outside it
  • How many different pairs of numbers can you remember that have a total of 20?
  • 20 = empty box + 13

Teaching guidance

This teaching guidance document suggests some of the key vocabulary, models, images and practical equipment that children should experience and be able to use. It also includes some teaching tips to provide a few starting points for ways of supporting children with this area of mathematics.

PDF file Can I recall all pairs of numbers that total 20? - teaching guidance | 65KB new window

Consolidation and practice

These resources are to support children in guided or independent work.

PDF file ITP Guide | 4317KB new window

SWF file Number facts ITP | 38KB new window

PDF file Addition and subtraction facts to 20 models and images chart | 164KB new window

PDF file Complements to 20 board | 16KB new window

Opportunities to use and apply

Possible contexts include:

  • Using inverse operations, e.g. I thought of a number and subtracted 6. The answer was 14. What was my number? How do you know?
  • Word problems, e.g. write numbers in the boxes to make these number stories true:
    Petra has empty box beetles and Kate has empty box beetles. Altogether they have 20 beetles.
    There are 20 people in the lift. empty box get out, empty box are left.
  • Finding all possibilities, e.g. using a set of 0–20 number cards, how many different pairs can you find that total 20?

Confirming learning

Ask probing questions such as:

  • Anna says she can think of ten different pairs of numbers that have a total of 20. How can you find out whether she is right?
  • Write one of these numbers into each box to make an addition sentence totalling 20.
    5, 9, 14, 3, 15, 17
    empty box + empty box = 20
    Are there different ways to do it?
  • How does 6 + 4 = 10 help you to find a related pair of numbers that total 20?
  • Fill in the missing numbers for these pairs that total 20:
    14 + empty box = 20
    4 + empty box = 20
    16 + empty box = 20
    6 + empty box = 20
    What do you notice?
  • What number sentences can you say and write using 5, 20 and 15?