Rounding, Skip Counting, Odd and Even

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What this lesson covers

  • The ones digit tells you which way to round to the nearest ten.
  • Counting in 2s and counting in 5s both land on the tens.
  • Counting in 3s goes odd, even, odd, even.
  • Numbers ending in 0, 2, 4, 6 or 8 are even; ending in 1, 3, 5, 7 or 9 are odd.
Key idea

Rounding to the nearest ten

  • 43 sits between 40 and 50 on a number line. It is closer to 40.
  • Look at the ones digit. 0, 1, 2, 3 or 4: round down. 5, 6, 7, 8 or 9: round up.
  • A ones digit of 5 is exactly halfway, and we round it up.
NumberOnes digitRounds to
43340
67770
85590
988100
1122110
Key idea

Skip counting from any number

  • You can start a count anywhere, not only at 0.
  • Counting in 2s from 7: add 2 each time.
  • Counting back in 5s from 63: take away 5 each time.
CountNumbers
on in 2s from 77, 9, 11, 13, 15
back in 5s from 6363, 58, 53, 48, 43
on in 10s from 3434, 44, 54, 64, 74
back in 10s from 104104, 94, 84, 74, 64
Key idea

Try it: skip count on and back

Key idea

Odd and even

  • Even numbers make pairs with none left over. Odd numbers have one left over.
  • Only the last digit matters.
  • 116 ends in 6, so it is even. 103 ends in 3, so it is odd.
Ends inThe number is
0, 2, 4, 6 or 8even
1, 3, 5, 7 or 9odd
Key idea

Try it: odd or even?

Worked example

Counting in 3s

  • Start at 3 and add 3 each time.
  • Look at the pattern: odd, even, odd, even.
  • You can start at any number in the count, like 30: 30, 33, 36, 39.
Count in 3sOdd or even
3odd
6even
9odd
12even
15odd
18even
Key idea

Where two counts meet

  • Counting in 2s: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20.
  • Counting in 5s: 5, 10, 15, 20.
  • Both counts land on 10 and 20. They meet on every ten.
NumberIn the 2s count?In the 5s count?
10yesyes
15noyes
16yesno
20yesyes
Key idea

Maths blocks

Common mistakes

  • 45 rounds to 40.
    A ones digit of 5 rounds up, so 45 rounds to 50.
  • 107 is even, because it has a 0 in it.
    Only the last digit matters. 107 ends in 7, so it is odd.
  • Counting back in 5s from 42: 42, 37, 33.
    Take away 5 every time: 42, 37, 32, 27.

Your turn

1

Round 76 to the nearest ten.

2

Is 113 odd or even?

3

Count on in 3s: 12, 15, 18, ?

4

Count back in 10s: 96, 86, 76, ?

5

Which number is in both the 2s count and the 5s count: 15, 20 or 25?

Show answer

1. 80 2. odd 3. 21 4. 66 5. 20

Summary

What to take away

  • Round with the ones digit: 5 or more rounds up.
  • Skip counts can start at any number and go either way.
  • The last digit tells you odd or even.
  • The 2s and 5s counts meet on the tens.
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More in Number

Numbers to 120: Read, Write and CompareNotesGroups of Ten and Where Numbers Sit on a LineNotesRounding, Skip Counting, Odd and EvenNotesAdding and Taking Away: Facts to 20 and TensNotesStory Problems: Adding and Taking Away to 100NotesTimes and Share: 2s, 5s and 10sNotesHalves, Thirds and QuartersNotesComparing Fractions and Finding the WholeNotesNZ Coins and Notes: Count and Make MoneyNotes

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