Counting to 100 and Place Value

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What this lesson covers

  • The numbers from 0 to 100 come in order, each one more than the last.
  • A two-digit number is made of tens and ones.
  • Twenty, thirty, forty and the other tens end in -ty.
  • To compare two numbers, look at the tens first.
Key idea

Numbers go in order

  • Start at 0 and count: 0, 1, 2, 3, 4, 5.
  • Each number is one more than the number before it.
  • The counting line keeps going all the way to 100.
one less, the number, one more
BeforeNumberAfter
8910
192021
495051
9899100
Key idea

Tens and ones

  • Bundle 10 ice block sticks together and you have one ten.
  • 34 is 3 bundles of ten and 4 loose sticks.
  • The left digit counts the tens. The right digit counts the ones.
100 is ten tens
NumberTensOnes
3434
4747
6060
909
100100
Key idea

Try it: build a number with tens and ones

Key idea

The -ty numbers

  • -ty means tens. Sixty is six tens.
  • Say the tens word, then the ones: 53 is fifty-three.
  • Careful: 16 is sixteen, but 60 is sixty.
TensNumberWord
2 tens20twenty
3 tens30thirty
4 tens40forty
5 tens50fifty
6 tens60sixty
7 tens70seventy
8 tens80eighty
9 tens90ninety
Worked example

Count on and count back

  • You can start counting from any number.
  • Count on to go up. Count back to go down.
  • Watch the tens change when the ones pass 9 or 0.
Start atCount onCount back
1718, 19, 20, 2116, 15, 14, 13
4243, 44, 45, 4641, 40, 39, 38
6869, 70, 71, 7267, 66, 65, 64
Key idea

Try it: find numbers on the hundred chart

Worked example

Which is bigger?

  • Look at the tens first. More tens means a bigger number.
  • If the tens are the same, look at the ones.
  • Positions have an order too: in a race, 2nd comes before 5th.
NumbersBiggerWhy
38 and 52525 tens is more than 3 tens
64 and 6164same tens, 4 ones is more than 1
45 and 54545 tens is more than 4 tens
9 and 90909 tens is more than 0 tens
Key idea

Try it: count on and back to 100

Common mistakes

  • Sixteen and sixty are the same number.
    16 is one ten and six ones. 60 is six tens.
  • Forty-two is written 402.
    Forty-two is 4 tens and 2 ones, so write 42.
  • After 29 comes 20.
    After 29 comes 30. Nine ones and one more make a new ten.
  • The 5th child in the line is closer to the front than the 2nd.
    The 2nd child is closer to the front. 2 comes before 5.

Your turn

1

How many tens and ones are in 58?

2

What number comes after 39?

3

Count back: 71, 70, __

4

Which is bigger, 45 or 54?

5

Write seventy-three as a number.

Show answer

1. 5 tens and 8 ones 2. 40 3. 69 4. 54 5. 73

Summary

What to take away

  • Numbers from 0 to 100 go in order.
  • Tens on the left, ones on the right.
  • -ty means tens.
  • Compare the tens first, then the ones.
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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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