Commutative law

Story: Monkey king and peaches Arithmetic Calculation Operation How do you feel? Explain it in maths

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

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

Task 1 Can you give other examples like this?

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

Task 1 Algebraically: a + b = b + a

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

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 the numbers being added and their sum remains the same.

Task 2 Does any other operation have commutative law? Show examples of each operations

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

Can you draw a diagram to show it? Task 2 Algebraically: a × b = b × a Can you draw a diagram to show it?

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

EXERCISE

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) □+△+○= □+○+△。（ ） × × × √

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

3、 QUICK CACULATION (STEP BY STEP) 28＋45＋72      62＋38＋123  67+（151+33) 8×23×125 25×43×40 =67+151+33 =67+33+151 =100+151 =251 =28+72+45 =100+45 =145 =62+38+123 =100+38 =138 =25×40×43 =1000×43 =43000 =8×125×23 =1000×23 =23000

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

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?

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

Summary What have you learned today?