(1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16
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Transcript of (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16
![Page 1: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/1.jpg)
(1) 1.5×28+72×1.5 (2) 48÷ ( 3×2+18 ) (3) 35×34+66×65 (4) 1.25×16 (5) 100-3.5-5.5 (6) 78+36+22 (7) 720÷36÷2 (8) 5×14-25×14
![Page 2: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/2.jpg)
![Page 3: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/3.jpg)
a+b=b+a加法交换律:
加法结合律:(a+b)+c=a+(b+c)
两个加数交换位置,和不变。
三个数相加,先把前两个数相加,或者先把后两个数相加,和不变。
![Page 4: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/4.jpg)
187+349+113=
86+75+125=
85+126+15+74=
★36+65=
365+199=
349 + ( 187+113 )86+ ( 75+125 )
( 85+15 ) + ( 126+74 )
( 36+64 ) +1
365-200+1
写出巧算的第一步( 练习纸第一题 A 组 )
![Page 5: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/5.jpg)
a-b-c=a-(b+c)
一个数连续减去两个数,可以减去这两个数的和。a-b-c=a-c-b
一个数连续减去两个数,交换两个减数的位置,差不变。
![Page 6: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/6.jpg)
75.93-8.47-1.53 =
12.8-6.5-2.5=
46-2.9-3.1=
81-10.3=
36.3-1.5-6.3=
75.93-(8.47+1.53)
12.8-(6.5+2.5)
46-(2.9+3.1)
81-10-0.3
36.3-6.3-1.5
![Page 7: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/7.jpg)
145- ( 45-30 ) 145-( 45+30 )
+ ( )直接去括号;- ( )去掉括号改变符号。
=145-45+30 =145-45-30
(利用减法的性质去括号时要注意变符号。)
![Page 8: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/8.jpg)
a×b=b×a乘法交换律:
乘法结合律:
乘法分配律:
(a×b) ×c=a× (b×c)
a×(b+c)= a×b+a×c
a×(b-c)= a×b-a×c
(反过来也可以运用)
![Page 9: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/9.jpg)
6×25×0.4=
23×5+77×5=
1.3×3.8+1.3×6.2=
58×8+43×8-8=
2.5×1.25×0.8×0.4=
2.5× ( 4+0.4)=
6×(25×0.4 )
(23+77)×5
1.3×(3.8+6.2)
( 58+43-1 ) ×8
2.5×1.25×0.8×0.4
2.5×4+2.5×0.4
![Page 10: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/10.jpg)
a÷b÷c=a÷ (b×c)
一个数连续除以两个数,可以除以这两个数的积。
a÷b÷c=a÷c÷b
一个数连续除以两个数,交换两个除数的位置,商不变。
![Page 11: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/11.jpg)
商不变的性质a÷b =(a×c)÷(b×c)
a÷b =(a ÷ c)÷(b÷c)
( c≠0 )
![Page 12: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/12.jpg)
300÷25÷4 300÷25
=300÷(25×4 ) = ( 300×4 ) ÷ ( 25×4 )
(除法性质及商不变的性质注意带括号,变符号)
(不用算结果,只要说出简便算的第一步)
这里你想提醒大家注意什么?
![Page 13: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/13.jpg)
25×4÷25×4 64-39+36
在加减混合、乘除混合运算简便算时你想提醒大家什么?
=25÷25×4×4=1×4×4=16
=64+36-39=100-39=61
(在加减混合、乘除混合运算简算中可以交换数的位置,交换时要看清运算符号,带符号一起搬家)
![Page 14: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/14.jpg)
(没有相同因数,但如果因数中存在倍数关系,就能创造相同因数进行简算)
360×5+64×50 1.3×32+2.6×34
=360×5+640×5=(360+640)×5=1000×5=5000
=1.3×32+1.3×68=1.3×(32+68)=1.3×100=130
你能用简便方法计算下列题目吗?
![Page 15: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/15.jpg)
(把其中一个因数改写成两个数相加减的形式,利用的是乘法分配律,改写后一定要打括号;如果改写成两数相乘的形式,利用的是乘法结合律,改写后可以不打括号)
1.25×88 38×103=1.25×8×11=10×11=110
=38× ( 100+3 )=38×100+38×3=3800+114=3914
![Page 16: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/16.jpg)
一、在 里和横线上填写相应的运算符号和数 .
868 - 5.2 - 4.8=868 (5.2 + )
1500 - 28 - 272= - (28 272)
684 - (584+37)=
- 4.8
1500 +
684 - 584 - 37
7.5 ÷2 ÷5=7.5 (2 5)÷ ×
1.4÷1.25÷0.8= ÷ ×1.4 (1.25 8 )
7.2÷(3.6×4)=7.2 3.6 4÷ ÷
![Page 17: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/17.jpg)
二、基础练习。1 . A+B+C=A+□+B 运用( )。2 . 436-(136+208)=436-□-□ 运用了( )。3 .◆ × ×■ ☆ = ×◆ (☆ ×■ ) 运用了( )。4 .( 25+125 ) ×8=□×□+□×□ 运用了( )。
加法交换律
减法性质
乘法结合律
乘法分配律
![Page 18: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/18.jpg)
三、辩错题。①101×56=100×56+1 ( )②123-68+32=123- ( 68+32 ) ( )③25× ( 8×4 ) =25×8+25×4 ( )④7÷1.25=7×8÷1.25×8 ( )⑤(3+0.8)×125=3×125+0.8 ( )
×
×
×
×
×
![Page 19: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/19.jpg)
278+498 145-97 25×4÷25×4 64-39+36 ( 36+48 ) ÷6 60÷ ( 10+5 ) 145- ( 45-30 ) 145- ( 45+30 ) 300÷25÷4 300÷25 360×5+64×50 13×32+87×34 125×88 38×103
四、看看以下这些计算题哪些能够简便计算?哪些不能简算?能简算的依据是什么?不能简算的应该按照什么顺序进行计算。
![Page 20: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/20.jpg)
648-126-274-148=
8157-(103+157+597)=
★ 123-38+77=
★ 176-65+165=
863-699=
★626-(326-174)=
648-148-(126+274)
8157-157-(103+597)
123+77-38
863-700+1
176+165-65
626-326+174
( B 组 : 写出巧算的第一步)五、
![Page 21: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/21.jpg)
( 1 ) 58×8+43×8-8=
( 2 ) 40.4×2.5=
( 3 ) 55×3÷5=
( 4 ) 183+98=
★ ( 5 ) 3.5×35+64×3.5+3.5 =
★ ( 6 ) 200-98-96=
8×(58+43+1)
10.1×(4×2.5)
55÷5×3
183+200 -2
3.5×(35+64+1)
200-100-100 +2+4
( C 组:写出巧算的第一步)
![Page 22: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/22.jpg)
75.93-8.47-1.53 =
12.5-6.8-2.5=
4600÷25÷4=
810÷45=
360÷5÷6=
4.1÷0.25=
3.2÷1.25=
75.93-(8.47+1.53)
12.5-(6.8+2.5)
4600÷(25×4)
810÷9÷5
360÷6÷5
(4.1×4) ÷(0.25×4)
( 3.2×8)÷(1.25×8)
(说说巧算的第一步)
![Page 23: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/23.jpg)
你还记得这些运算定律吗?
加法交换律加法结合律乘法交换律乘法结合律乘法分配律
减法的性质
除法的性质
a + b = b + a(a + b) + c = a + (b + c)a ×b = b ×a(a ×b) ×c = a×(b ×c)
(a + b) ×c = a ×c + b ×c
a - b - c = a - (b + c)a - b - c = a - c - b
a ÷b ÷ c = a ÷(b ×c)
a ÷b ÷ c) = a ÷ b ÷ c
![Page 24: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/24.jpg)
125×26×8 17×4×25
125× ( 8×5 ) 25×16×125
64×53+36×53 7.2÷0.125
23×125-15×125 3÷0.25÷4
16×80+8×540 9.6÷(0.96×2)
25×10.4 36×9.9 36×9.9
74×99+74 3.2×25
![Page 25: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/25.jpg)
(1) 7.2÷0.125 (2) 3÷0.25÷4 (3) 9.6÷(0.96×2) (4) 2.7-1.2-0.8 (5) 3.6+1.5+26.4+3.5 (6) 4.8-2.9-1.1 (7) 7.38-(2.4+1.38)-1.6 (8) 2.4×125+5.6×125 (9) 25×3.2×125 (10) 25×(0.8+4)×125 (11) 6.6×3÷6(12)(1.2×2+1.2×6) ×125 (13) 0.06+9.5× 〔 0.4×(40.75-9.5 〕 (14) 0.81×0.9+0.81÷0.9
递等式计算 ( 能简便计算的要能简便计算 )
![Page 26: (1) 1.5×28+ 7 2×1.5 (2) 48÷(3×2+18) (3) 35×34+66×65 (4) 1.25×16](https://reader036.fdocuments.net/reader036/viewer/2022062314/56813698550346895d9e29ee/html5/thumbnails/26.jpg)
(五)最佳创意:从以下 6 个数中,任选 3-4 个,编写一道能简便计算的算式。
16 4 200 2.5 3.5 8