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b) 3.25.8+ 4.37.6+2.38.12
= 24.25+24.37+24.38
=24.(25+ 37+38)
=24.100
=2400
c) (563+745)-(463+545)
= (563-463)+(745+545)
= 100 + 100
= 200
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( x - 15 ) x 7 - 270 : 45 = 169
( x - 15 ) x 7 - 6 = 169
( x - 15 ) x 7 = 175
x - 15 = 25
x = 40
( x-15 ) x7 - 270 : 45 = 169
( x - 15) x 7 =169 x 45
( x - 15) x 7 =7605
x - 15 =7605 : 7
x - 15 =7620
x =7620 + 15
x
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\(A=2\times4+4\times6+...+98\times100\)
\(A=2.2+2.12+...+2.149\)
\(A=2.\left(2+12+...+149\right)\)
Tự làm nốt( dấu x = dấu chấm )
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( 1 - 3/10 - x ) : ( 19/10 - 1 - 2/ 5 ) + 4/5 = 1
=> (7/10 - x) : (9/10 - 2/5) = 1 - 4/5
=> (7/10 - x) : 1/2 = 3/5
=> (7/10 - x) = 3/5 : 1/2
=> 7/10 - x = 6/5
=> x = 7/10 - 6/5
=> x = -1/2
ko ghi lại đề
=>(7/10-x):1/2+4/5=1
=>(7/10-x):1/2=1/5
=>7/10-x=1/10
=>x=3/5
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\(x\times9,6+x:2,5=45\\ x\times9,6+x\times0,4=45\\ x\times\left(9,6+0,4\right)=45\\ x\times10=45\\ x=45:10\\ x=4,5\)
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4 x 113 x 25 - 5 x 112 x 20
= 100 x 113 - 100 x 112
= 100 x (113 - 112)
= 100 x 1
= 100
2154*10+6875*10
=(2154+6875)*10
=9029*10
=90290
120/4*45+68
=30*45+68
=1350+68
=1418
=10 x (2154+6875)=10 x 9029=90290