Groups, Pairs and Counting in 2s and 10s

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What this lesson covers

  • You can see a small group and know how many without counting.
  • Ten ones make one ten.
  • The same number can be grouped in different ways.
  • Counting in 2s from an even number gives even numbers; from an odd number gives odd numbers.
Key idea

See it without counting

  • Look at a dice. You know 5 dots without counting them.
  • In a group of 8 dots, you might see 5 and 3.
  • Small groups you know help you find the total fast.
You seeYou know
4 dots and 2 dots6
5 dots and 3 dots8
5 dots and 5 dots10
3 dots and 3 dots6
Key idea

Try it: fill the ten frames

Key idea

Ten ones make one ten

  • Count 10 pāua shells and put them in one pile. That pile is one ten.
  • The same number can be shown in different groups.
  • 12 is still 12, however you group it.
12 asLooks like
12 ones12 single shells
six pairs2, 4, 6, 8, 10, 12
one ten and two onesa pile of 10 and 2 more
Worked example

Count in pairs, 5s and 10s

  • Point to each thing once and say one number: 1, 2, 3.
  • Faster: count shoes in pairs, fingers in 5s, and full ten frames in 10s.
  • Every way gives the same total.
ThingsCount inSayTotal
16 sockspairs2, 4, 6, 8, 10, 12, 14, 1616
15 fingers5s5, 10, 1515
20 counters10s10, 2020
Key idea

Try it: put them in pairs

Key idea

Even and odd

  • Count in 2s from 0: 0, 2, 4, 6, 8, 10. These are even numbers.
  • Count in 2s from 1: 1, 3, 5, 7, 9. These are odd numbers.
  • Even numbers end in 0, 2, 4, 6 or 8.
Start atCount in 2sThese are
00, 2, 4, 6, 8even
11, 3, 5, 7, 9odd
1414, 16, 18, 20even
2727, 29, 31, 33odd
Worked example

Hop in 2s and 10s from any number

  • Counting in 10s, the ones digit stays the same.
  • Counting in 2s, you skip every other number.
  • You can hop backwards too.
StartHopCount
34on 2s34, 36, 38, 40
50back 2s50, 48, 46, 44
23on 10s23, 33, 43, 53
86back 10s86, 76, 66, 56
Key idea

Try it: hop in 2s and 10s

Common mistakes

  • Counting in 2s from 3 gives even numbers.
    3, 5, 7, 9 are odd. Start on an odd number and you stay odd.
  • Counting in 10s from 23 goes 23, 30, 40.
    The ones stay the same: 23, 33, 43.
  • 12 can only be twelve ones.
    12 is also six pairs, or one ten and two ones.
  • Counting back in 2s: 40, 39, 38.
    Skip a number each time: 40, 38, 36.

Your turn

1

Count on in 2s: 14, 16, 18, __

2

Count back in 10s: 75, 65, 55, __

3

There are 9 pairs of socks. How many socks is that?

4

Is 17 odd or even?

5

A group has 5 dots and 3 dots. How many dots altogether?

Show answer

1. 20 2. 45 3. 18 4. Odd 5. 8

Summary

What to take away

  • Spot small groups instead of counting one by one.
  • Ten ones make one ten.
  • Hop in 2s and 10s, forwards and backwards.
  • Even numbers end in 0, 2, 4, 6 or 8.
Report a mistake

More in Number

Counting to 100 and Place ValueNotes1st, 2nd, 3rd, Te Reo Numbers and Number LinesNotesGroups, Pairs and Counting in 2s and 10sNotesNumber Facts to 10, Doubles and Adding to 20NotesJoining, Taking Away and Equal GroupsNotesHalves and QuartersNotesSharing Fairly: From Halves to QuartersNotesNew Zealand Coins and NotesNotes

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