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2020 x 2021 - 3031 = 2020 x ( 2 + 2019 ) - 3031 = 2020 x 2019 + 2020 x 2 - 3031 = 2019 x 2020 + 1009
Nên ( 2019 x 2020 + 1009 ) : ( 2020 x 2021 - 3031 ) = ( 2019 x 2020 + 1009 ):( 2019 x 2020 + 1009 )=1
\(=\dfrac{2019\cdot2020\left(2020\cdot10001-2019\cdot10001\right)}{2020\cdot2019\cdot2018\cdot10001}=\dfrac{10001\cdot1}{10001\cdot2018}=\dfrac{1}{2018}\)
\(A=\frac{2}{2018\times2020}+\frac{2021}{2020}-\frac{2019}{2018}\)
\(A=\frac{2020-2018}{2018\times2020}+\frac{2021}{2020}-\frac{2019}{2018}\)
\(A=\frac{1}{2018}-\frac{1}{2020}+\frac{2021}{2020}-\frac{2019}{2018}\)
\(A=\left(\frac{2021}{2020}-\frac{1}{2020}\right)-\left(\frac{2019}{2018}-\frac{1}{2018}\right)\)
\(A=1-1=0\)
3,42 : 0,2 + 3,42 : 0,5 + 3,42 : 0,25 - 3,42
=3,42 : \(\frac{1}{5}\) + 3,42 : \(\frac{1}{2}\) + 3,42 : \(\frac{1}{4}\) - 3,42
=3,42 x 5 + 3,42 x 2 + 3,42 x 4 - 3,42
=3,42 x (5+2+4-1)
=3,42 x 10
=34,2
Học tốt
13,25 : 0,5 + 13,25 : 0,2 + 13,25 : 0,25
=13,25 x 2 + 13,25 x 5 + 13,25 x 4
= 13,25 x ( 2+5+4)
=13,25 x 11
=145,75
120 - 0,5 x 40 x 5 x 0,2 x 20 x 0,25 - 20
= ( 120 - 20 ) - [ ( 0,5 x 20 ) x ( 40 x 0,25 ) x ( 0,2 x 5 ) ]
= 100 - [ 10 x 10 x 1 ]
= 100 - 100
= 0
\(120-0,5\times40\times5\times0,2\times20\times0,25-20\)
\(=120-\left(0,5\times20\right)\times\left(40\times0,25\right)\times\left(5\times20\right)-20\)
\(=120-10\times10\times100-20\)
\(=120-10000-20\)
\(=-9900\)
\(2020:0,2+2020+2020:0,25\)
\(=2020:\dfrac{1}{5}+2020+2020:\dfrac{1}{4}\)
\(=2020\times5+2020+2020\times4\)
\(=2020\times \left(5+1+4\right)\)
\(=2020\times10\)
\(=20200\)