1. challenge
(1) ×75×40×2
(2) 125×25×32
(3) ( )×25

2. Law of Multiplication(2) Shanghai Luwan No.2 Primary School
Murphey Chen
陈默华

3. We have learned 4 Laws of Calculation
These laws only use in addition or multiplication.
1) the commutative law of addition
addition =
2) the associative law of addition
=69+( )
3) the commutative law of multiplication
multiplication
2×18×5 =2×5×18
4) the associative law of multiplication
18×5×2=18×(5×2)

4. addition and multiplication !
There are a law between
addition and multiplication !

5. What can you see?
How many apples are there in this picture?
Write your number sentence.

6. 5 threes is 15，
3 threes is 9，
15+9=24，
There are 24 apples.

7. 5 threes add 3 threes is 8 threes

8. What can you see?
How many apples are there in this picture?
Write your number sentence use the way we learned.

9. 3 sixs add 4 sixs is 7 sixs,7 sixs is 42！

10. Say and Write: 9 5 14
Think：( ) fours add ( ) fours equals ( ) fours. 9 5
Number sentence：( )×4 + ( )×4 = ( )×4=( ) 14 56

11. 5 8 13 Group of 2 in same colour and Fill in the blanks:
Think：( ) twos add ( ) twos equals ( ) twos. 5 8 13
5×2+8×2=13×2=26
Number sentence：

12. Circle and Calculate: Think： 2 threes add 4 threes equals 6 threes.
3 twos add 6 twos equals 9 twos.
1 six add 2 sixes equals 3 sixes.
2×3+4×3=6×3=18
Number sentence：
3×2+6×2=9×2=18
1×6+2×6=3×6=18

13. Can you find some secrets?
5×3+8×3=13×3
6×3+4×3=10×3
9×4+5×4=14×4
5×2+8×2=13×2
3×2+6×2=9×2
2×3+4×3=6×3
1×6+2×6=3×6 ●
the same model: □×□+□×□ ●
the same factor in two multiplications. ●
different factors add first, then do multiply.

14. Practice: 16×15+23×15=( )×15=( ) 1、25×23+15×23=( )×23=( )
16×15+23×15=( )×15=( ) 39
585
1、25×23+15×23=( )×23=( )
2、34×17+61×17=( )×17=( )
3、47×80+54×80=( )×80=( ) 40
920 95
1615
101
8080

15. 1、25×23－15×23=( )×23=( ) 2、61×17－34×17=( )×17=( )
Can you do these challenge?
1、25×23－15×23=( )×23=( )
2、61×17－34×17=( )×17=( )
3、85×80－47×80=( )×80=( ) 10
230 27
459 38
3040

16. 2×3＋8×3=10×3=30
1×6＋4×6=5×6=30

17. 2×3＋8×3=10×3=30
1×6＋4×6=5×6=30