Times and Share: 2s, 5s and 10s

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What this lesson covers

  • Groups and arrays show multiplying and dividing.
  • × 1 and ÷ 1 keep a number the same; × 0 always gives 0.
  • You can multiply in either order, but not divide.
  • Multiplying and dividing undo each other.
Key idea

Groups of the same

  • 3 bags with 5 apples in each. Count in 5s: 5, 10, 15.
  • We write this as 3 × 5 = 15. Say "3 groups of 5".
  • The sign × means groups of. It is multiplying.
Worked example

Skip counting and times facts

  • Each skip count is a times fact. Count how many skips you made.
Count inSkip countFact
2s2, 4, 6, 84 × 2 = 8
5s5, 10, 15, 20, 255 × 5 = 25
10s10, 20, 30, 40, 50, 606 × 10 = 60
Key idea

Maths blocks

Key idea

Arrays

  • An egg carton has 2 rows of 6 eggs: 2 × 6 = 12.
  • Turn the carton around: 6 rows of 2. Still 12 eggs.
  • So 2 × 6 and 6 × 2 are the same. Order does not matter when you multiply.
  • Dividing is different. 12 ÷ 2 is 6, but 2 ÷ 12 is less than 1.
Key idea

Sharing undoes multiplying

  • 10 strawberries shared between 2 friends: 5 each. 10 ÷ 2 = 5.
  • The sign ÷ means share or split into equal groups.
  • Multiplying and dividing undo each other: 5 × 2 = 10, so 10 ÷ 2 = 5.
Times factSharing facts
5 × 2 = 1010 ÷ 2 = 5 and 10 ÷ 5 = 2
4 × 10 = 4040 ÷ 10 = 4 and 40 ÷ 4 = 10
Key idea

Try it: share them out

Key idea

Zero and one

  • 7 × 1: one group of 7. Still 7.
  • 7 ÷ 1: 7 shared with one person. They get all 7.
  • 7 × 0: zero groups of 7. Nothing at all, so 0.
SumAnswerSay it
7 × 17one group of 7
7 ÷ 177 shared with 1 person
7 × 00no groups
0 × 100no groups of 10
Worked example

Facts up to 100

  • Use the 2s, 5s and 10s you know.
FactUndo it
9 × 5 = 4545 ÷ 5 = 9
8 × 2 = 1616 ÷ 2 = 8
7 × 10 = 7070 ÷ 10 = 7
10 × 10 = 100100 ÷ 10 = 10

Common mistakes

  • 6 × 0 = 6, just like 6 + 0.
    6 × 0 means 6 groups of nothing, so it is 0.
  • 10 ÷ 2 is the same as 2 ÷ 10.
    Order matters when you divide. 10 ÷ 2 = 5, but 2 shared between 10 is less than 1 each.
  • 3 × 5 means 3 + 5.
    3 × 5 means 3 groups of 5, so it is 15, not 8.

Your turn

1

7 × 2 = ?

2

4 × 5 = ?

3

60 ÷ 10 = ?

4

9 × 1 = ?

5

35 ÷ 5 = ?

Show answer

1. 14 2. 20 3. 6 4. 9 5. 7

Summary

What to take away

  • Skip counting is multiplying.
  • × 1 keeps the number; × 0 makes 0.
  • Multiply in any order; divide in one order.
  • Sharing undoes multiplying.
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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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