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x : 84 = 124 42 x \(x\)= 1890
x = 124 x 84 x = 1890 : 42
x = 10.416 x = 45
x : 84 = 124
=> x = 124 x 84 = 10416
42 . x = 1890
=> x = 1890 : 42 = 45
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= 1890 x ( 1558 + 454 ) - 1006 x 1780
= 1890 x 2012 - 1006 x 1780
= 1890 x 1006 x 2 - 1006 x 1780
= 1006 x ( 1890 x 2 - 1780 )
= 1006 x 2000
= 2012000
1558x1890+1890x454-1006x1780
=1890(1558+454)-1006x1780
=1890x2012-1006x1780
=1890x2x1006-1006x1780
=1006(1890x2-1780)=1006x2000=1006x1000x2
=1006000x2=2012000.
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a) ( 45 + 12 ) + ( 2012 - 120 - 45 )
= 45 + 12 + 2012 - 120 - 45
= 57 + 2012 - 120 - 45
= 2069 - 120 - 45
= 1976 - 45
= 1931
b) ( 1890 - 19 - 5 ) - ( 19 - 5 + 1890 )
= 1890 - 19 - 15 - 19 - 5 + 1890
= 1871 - 15 - 19 - 5 + 1890
= 1856 - 19 - 5 + 1890
= 1837 - 5 + 1890
= 1832 + 1890
= 3722
a, (45+12) + (2012-120-45)
= 45+12+2012-120-45
=(45-45) + 2012-120+12
=0+1892+12
=1904
b, (1890-19-5) - (19-5+1890)
=1890-19-5+19+5-1890
=(1890-1890)+(-19+19)+(-5+5)
=0