Transcript Commutative law

Story:
The Monkey king and the peaches
Can you express the sum
of the peaches in two
How do you feel?
different number
sentences?
What is the same? What is different?
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 are
there in total?
Task 1
Can you think of any other
examples like this?
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
Task 1
Letter expression:
a + b = b + a
Game Time
I say 1+2
you say 2+1
follow-up exercises
Fill in the blanks by using the commutative law of addition
256＋214= 214 ＋256
X+Y=
△+☆=
y
＋X
☆ ＋ △
十 367=367 ＋
1
5
……
1
5
Add two numbers, exchange the
position of addends and their sum
remains the same.
Task 2
We now know
the commutative law of addition.
Are there commutative laws
with other operations?
Please Guess！
In subtraction, can we use the
commutative law ?
18 - 3
18 ÷ 3
3 - 18
3 ÷ 18
Task 2
Multiply two numbers. Exchange
the position of the factors and
their product remains the same.
commutative law of multiplication
Task 2
Letter expression:
a × b = b × a
Fill in the blanks by using the
commutative law of multiplication
34×71= 71 × 34
45×55 =55×45
■ ×▲= ▲ ×■
D × C =C×D
Multiply two numbers. Exchange
the position of factors and their
product remains the same.
EXERCISE
1、True or false?
(1) 56+38=83+56 is using the commutative
law of addition.（× ）
(2) 2×3=1×6 is using the commutative law of
multiplication. （× ）
(3) A×B=B+A。（×）
(4) □+△+○= □+○+△。（ √ ）
2、Fill in the blanks by using the
commutative law
52×（ 141 ）=141 ×（ 52 ）
55+87+45=55+（ 45 ）+87
☆+（●）=●+（☆）
25×18×4=（25 ）×（4 ）×（18）
△×（☺ ）×★=（△）×★×☺
3、Solve by making the question simpler
28＋45＋72
=28+72+45
=100+45
=145
62＋38＋123
=62+38+123
=100+38
=138
8×23×125
=8×125×23
=1000×23
=23000
67+（151+33)
=67+151+33
=67+33+151
=100+151
=251
25×43×40
=25×40×43
=1000×43
=43000
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
Using your brain:
John and Lucy are calculating
98 ＋ 998 ＋ 9998 ＋ 2 × 3,
John said the correct answer right away.
Can you？
Summary
What have you learned today？