1. Laws of operation

2. Monkey king and peaches
Story:
Monkey king and peaches
8000
10815
0.2961
How do you feel?
Explain it in maths

3. Find similarities and differences
3+4= =7
3+4=4+3

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

5. Task 1
Can you give other examples like this?

6. commutative law of addition
Task 1
Add two numbers, exchange the place of addends and their sum remains the same.
commutative law of addition

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

10. Task 2
Does any other operation have commutative law?

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

12. Task 2
a × b = b × a

13. 34×71= × 45× =55× ×▲= ×■ × =C×D 71 34 55 45 ■ ▲ D C
Fill in the blanks by using
commutative law of multiplication
34×71= × × =55×
×▲= ×■ × =C×D 71 34 55 45 ■ ▲ D C
Multiply two numbers. Exchange the places of factors and their product remains the same.

14. EXERCISE

15. 1、true or false： 56+38=83+56 is using the commutative
law of addition.（ ）
2×3=1×6 is using commutative law of
multiplication. （ ）
(3) A×B=B+A。（ ）
(4) □+△+○= □+○+△。（ ） × × × √

16. 2、Fill in the blanks by using commutative law
52×（ ）=141 ×（ ）
=55+（ ）+87
☆+（ ）=●+（ ）
25×18×4=（ ）×（ ）×（ ）
△×（ ）×★=（ ）×★×☺
141 52 45 ● ☆ 25 4 18 ☺ △

17. 3、 QUICK CACULATION (STEP BY STEP)
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

18. 4、Solve the problem
Miss White bought gifts for the class, the class has 25 students and each present need 12 pounds, how much does Miss White pay altogether?
25×12
=25×4×3
=100×3
=300

19. 5. Alex is going to have a party at home
5. Alex is going to have a party at home. His Mum bought 2 dozens of coke, 32 apples, 24 bananas and 8 peaches. How many fruits did she buy?

20. Try your best:
John and Lucy are calculating
98 ＋ 998 ＋ 98 ＋ 2 × 3,
John find the correct answer right away. Can you?

21. Let’s play a game. （1）70、50、30 （2）32、40、68 （3）100、150、850
Find the sum of three numbers in least time.
（1）70、50、30
（2）32、40、68
（3）100、150、850
Add up to the tens 、hundreds or thousands

22. Task 3
63＋55＋45
=（63＋55）＋45
= 118＋45
= 163
63＋55＋45
=63＋（55＋45）
=63＋100
=163
What are the similarities and differences between two number sentences?
（63＋55）＋45=63＋（55＋45）

23. Task 3 （27+36）+64=27+（36＋64） Which method is best? WHY? 27＋36＋64
=27＋（36＋64）
=27＋100
=127
=（27＋36）＋64
= 63＋64
= 127
（27+36）+64=27+（36＋64）

24. Who can give some examples like this?
Task 3
（63＋55）＋45=63＋（55＋45）
（27+36）+64=27+（36＋64）
Who can give some examples like this?

25. associative law of addition
Task 3
Add three numbers.
Add the first two numbers and then add the third number.
Or add the last two numbers and then add the first number.
Their sum remains the same.
associative law of addition

26. Task 3
(a + b)+c = a+(b + c)

27. follow-up exercises （33＋16）＋84= ＋（16＋ ） （168＋24）＋76= ＋（ ＋ ）
Fill in the blanks by using associative law of addition
（33＋16）＋84= ＋（16＋ ）
（168＋24）＋76= ＋（ ＋ ）
（25＋ ）＋72= ＋（28＋72）
（a＋ ）＋c=a＋（b＋ ） 33 84 24 76
168 28 25 c b

28. Task 4
Danny's father bought 3 boxes of juice, 25 cans per box, each can cost £4 ，how many did his father pay totally?
3×25 ×4

29. Task 4 3×25×4 3×25×4 =（3×25）×4 =3×（25×4） = 75×4 =3×100 = 300 =300
= 75×4
= 300
3×25×4
=3×（25×4）
=3×100
=300
What can you find?
（3×25）×4= 3×（25×4）

30. Task 4 26×8×125 =26×（8×125） 26×8×125 =（26×8）×125 = 208×125 =26×1000
26×8× =26×（8×125）
26×8×125
=（26×8）×125
= 208×125 =
=26×1000
=26000
（26×8）×125= 26×（8×125）

31. Who can give some examples like this?
Task 4
（3×25）×4= 3×（25×4）
（26×8）×125= 26×（8×125）
Who can give some examples like this?

32. associative law of multiplication
Task 4
Multiply three numbers.
Multiply the first two numbers and then multiply the third number.
Or multiply the last two numbers and then multiply the first number.
Their product remains the same.
associative law of multiplication

33. Task 4
(a × b)×c = a×(b × c)

34. follow-up exercises 36×(71×26)=（ ____ × _____ ）×26
Fill in the blanks by using associative law of addition
36×(71×26)=（ ____ × _____ ）×26
(57×95)×83=57×（ ____ × ____ ）
●×▲×★=___ ×（▲× __ ）
=（ ___ × ▲）× ____ 36 71 95 83 ● ★ ● ★

35. (a ＋ b) ＋ c = a ＋ (b ＋ c)
(a × b) × c = a × (b × c)
Compare with the associative law of addition and multiplication，what do you find?
three numbers
calculate from left to right in turn
calculate the last two numbers first
the answer remain the same

36. Exercise

37. 1、Line the same number sentence
(1) a×（b×c） A. 24＋（42＋58）
(2) 76＋18＋ B. 76＋（18＋22）
(3) 24＋42＋ C. 67×（125×8）
(4)（67×125）× D. （a×b）×c

38. 2、Which number sentence conforms to the associative law?
(1) a×(b×c)=(a×b)×c  (2) 15＋(7＋3)=(15＋2)＋3
(3) (23+41)+72+28=23+41+(72+28) √ × √

39. 3、Fill in the blanks by using associative law
(1) 25＋34＋66=___＋（ ___＋____ ）
(2) 25×40×78=（ ____ × ____ ）×78
(3) 56＋72＋44=(___＋ ___)＋72
(4) 75×8×2×125=
（ ___ × ___ ）×（ ___ × ___ ） 25 34 66 25 40 56 44 8
125 75 2

40. 4、Quick Calculate step by step
92＋89＋11  ×39× ×17×8  
85＋41＋15＋ ×125
=39×5×2
=39×（5×2）
=39×10
=390
=92+（89+11）
=92+100
=192
=125×8×17
=1000×17
=17000 =
=（85+15）+（41+59） =
= 200
=8×8×125
=8×（8×125）
=8×1000
=8000