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\(\dfrac{2020}{2019}-\dfrac{2019}{2018}+\dfrac{1}{2019}x2018\)
\(=\dfrac{2020}{2019}-\dfrac{2019}{2018}+\dfrac{2018}{2019}=2-\dfrac{2019}{2018}=\dfrac{2017}{2018}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(128\times68+16\times256\)
\(=128\times68+16\times2\times128\)
\(=128\times68+32\times128\)
\(=128\times\left(68+32\right)\)
\(=128\times100=12800\)
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\(357:\left(87:x\right)=110\)
\(\Leftrightarrow87:x=\dfrac{357}{110}\)
\(\Leftrightarrow x=\dfrac{3190}{119}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(357:\left(87:x\right)=110\)
\(\Leftrightarrow87:x=\dfrac{357}{110}\)
hay \(x=\dfrac{3190}{119}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a: =472x2+472x5+472x2
=472x9=4248
b: =3,6x8+7,2x4+7,2x2
=7,2(4+4+2)
=72
d: =2,4(6,2+1,9x2)=24
a: =472x2+472x5+472x2
=472x9=4248
b: =3,6x8+7,2x4+7,2x2
=7,2(4+4+2)
=72
d: =2,4(6,2+1,9x2)=24
![](https://rs.olm.vn/images/avt/0.png?1311)
a: 4A=4+4^2+...+4^9
=>3A=4^9-1
=>A=(4^9-1)/3
b: 2A=1+1/2+...+1/2^7
=>A=1-1/256=255/256
c: =1-1/5+1/5-1/9+...+1/85-1/89
=1-1/89=88/89
d: =1/3(3/1*4+3/4*7+...+3/304*307)
=1/3(1-1/4+1/4-1/7+...+1/304-1/307)
=1/3*306/307=102/307
e: E=1-1/2+1/2-1/3+...+1/11-1/12
=1-1/12=11/12
g: =2/5(1-1/6+1/6-1/11+...+1/96-1/101)
=2/5*100/101=40/101
![](https://rs.olm.vn/images/avt/0.png?1311)
12,5 x4,8+12,5 x4,8+12,5
=12,5 x4,8+12,5 x4,8+12,5x1
=12,5 x (4,8+4,8+1)
=12,5 x 10,6
=132,5
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Answer:
a) 42% của 60kg
\(60\times42:100=25,2kg\)
b) 36,5% của 2ha
\(2\times36,5:100=0,73ha\)
TL:
Bài 1
a) 42% của 60 kg là :
60 : 100 x 42 = 25,2 kg
b) 36,5% của 2 ha là :
2 : 100 x 36,5 = 0,73 ha
= 128 x 68 + 16 x 2 x 128
= 128 x 68 + 32 x 128
= 128 x ( 68 + 32 )
= 128 x 100
= 12800