1. Commutative law

2. Story:
The Monkey king and the peaches
Can you express the sum of the peaches in two different number sentences?
How do you feel?

3. What is the same? What is different?
3+4= =7
3+4=4+3

4. How many cans of fruit juice are there in total?
Task 1
8+18=26
18+8=26
8+18=18+8
How many cans of fruit juice are there in total?

5. Can you think of any other
Task 1
Can you think of any other
examples like this?

6. commutative law of addition
Task 1
Add two numbers, exchange the position of the addends and their sum remains the same.
8+18=26
18+8=26
8+18=18+8
commutative law of addition

7. Task 1
Letter expression:
a + b = b + a

8. Game Time
I say 1+2
you say 2+1

9. follow-up exercises 214 y ☆ △ 1 1 5 5 …… 256＋214= ＋256 X+Y= ＋X △+☆= ＋
Fill in the blanks by using the commutative law of addition
256＋214=           ＋256
X+Y=          ＋X
△+☆=          ＋
十 367=367 ＋      
214 y ☆ △ 1 1 5 5 ……
Add two numbers, exchange the position of addends and their sum remains the same.

10. Task 2 Please Guess！ We now know the commutative law of addition.
Are there commutative laws
with other operations?
Please Guess！

11. In subtraction, can we use the commutative law ?
18 - 3
3 - 18 ？
18 ÷ 3
3 ÷ 18 ？

12. commutative law of multiplication
Task 2
Multiply two numbers. Exchange the position of the factors and their product remains the same.
commutative law of multiplication

13. Task 2
Letter expression:
a × b = b × a

14. 34×71= × 45× =55× ×▲= ×■ × =C×D 71 34 55 45 ■ ▲ D C
Fill in the blanks by using the
commutative law of multiplication
34×71= × × =55×
×▲= ×■ × =C×D 71 34 55 45 ■ ▲ D C
Multiply two numbers. Exchange the position of factors and their product remains the same.

15. EXERCISE

16. 1、True or false? 56+38=83+56 is using the commutative
law of addition.（ ）
2×3=1×6 is using the commutative law of
multiplication. （ ）
(3) A×B=B+A。（ ）
(4) □+△+○= □+○+△。（ ） × × × √

17. 2、Fill in the blanks by using the commutative law
52×（ ）=141 ×（ ）
=55+（ ）+87
☆+（ ）=●+（ ）
25×18×4=（ ）×（ ）×（ ）
△×（ ）×★=（ ）×★×☺
141 52 45 ● ☆ 25 4 18 ☺ △

18. 3、Solve by making the question simpler
28＋45＋72      62＋38＋123  （151+33)
8×23× ×43×40 = = =
=251 =
=100+45
=145 =
=100+38
=138
=25×40×43
=1000×43
=43000
=8×125×23
=1000×23
=23000

19. 4、Solve the problem
Miss Li bought gifts for her class. The class has 125 students and each present costs £16. How much will Miss Li pay in total?
125×16
=125×8×2
=1000×2
=2000

20. John said the correct answer right away.
Using your brain:
John and Lucy are calculating
98 ＋ 998 ＋ 9998 ＋ 2 × 3,
John said the correct answer right away.
Can you？

21. Summary
What have you learned today？