581 + (878 + 419) = (581 + 419) = 878 = 1000 + 878 = 1878

(689 + 875) + 125 = 689 + (875 + 125) = 689 + 1000 = 1689.

581 + (878 + 419) = (581 + 419) = 878 = 1000 + 878 = 1878.

a) (689 + 875) + 125

= 689 + (875 + 125)

= 689 + 1000 = 1689.

581 + (878 + 419)

= (581 + 419) = 878

= 1000 + 878 = 1878.

b)

c) 5,87 + 28,69 + 4,13

= (5,87 + 4,13) + 28,69

= 10 + 28,69

= 38,69.

83,75 + 46,98 + 6,25

= (83,75 + 6,25) + 46,98

= 90 + 46,98

= 136,98.

a)419  x 2 + 419 x 3 + 419 x 5

= 419 x ( 2 + 3 + 5 )

= 419 x 10

= 4190

b) 7020 x 7 - 7020 x 3 - 7020 x 4

= 7020 x ( 7 - 3 - 4 )

 = 7020 x 1

= 7020

a, 419 x ( 2 + 3 +5)

= 419 x 10 = 4190.

b, 7020 x ( 7 - 3 - 4)

= 7020 x 0 = 0.

\(\frac{5}{6}+\frac{7}{12}=\frac{10}{12}+\frac{7}{12}=\frac{17}{12}\)

\(3+\frac{5}{7}=\frac{21}{7}+\frac{5}{7}=\frac{26}{7}\)

(689+875)+125=689+875+125=689+1000=1689

581+(878+419)=581+878+419=581+419+878=1000+878=1878

5,87+28,69+4,13=5,87+4,13+28,69=10+28,69=38,69

83,75+46,98+6,25=83,75+6,25+46,98=90+46,98=136,98

5/6 + 7/12 = 17/12

3 + 5/7 =  26/7

926,83 + 549,67 = 1476.5

(689 + 875) + 125 = 689 + (875 + 125) = 1689

581 + (878 + 419) = (581 + 419) + 878 = 1878

5,87 + 28,69 + 4,13 = (5,87 + 4,13) + 28,69 = 38,69

83,75 + 46,98 + 6,25 =( 83,75 + 6,25) + 46,98 = 136,98

\(419:\left(8\times8\times4,18+0,17\times2,5+2,09\times2\times36+0,23\times2,5\right)\)

\(=419:\left(64\times4,18+0,17\times2,5+4,18\times36+0,23\times2,5\right)\)

\(=419:\left[\left(64+36\right)\times4,18+\left(0,17+0,23\right)\times2,5\right]\)

\(=419:\left[100\times4,18+0,4\times2,5\right]\)

\(=419:\left[418+1\right]\)

\(=419:419\)

\(=1\)

\(=\dfrac{419}{64\cdot4.18+0,17\cdot2,5+2,09\cdot72+0,23\cdot2,5}\)

\(=\dfrac{419}{0,4\cdot2,5+64\cdot4,18+2,09\cdot72}\)

\(=\dfrac{419}{1+418}=1\)

a,= (435+565)-(360+140)= 1000-500= 500

b,= (121+879)+(581+419)= 1000+1000= 2000

a) 435-360+565-140

=(435+565)-(360-140)

=1000-220

=780

b)121+581+879+419

=(121+879)+(581+419)

=1000+1000

=2000