A = (-5,85) + {[(+41,3)+(+5) + (+0,85))}

= {(-5,85) + [(+5) + (0,85)]} + (+ 41,3)

= {(-5,85) + (5,85)} + (+ 41,3)

= 0 + 41,3

= 41,3

B = (-87,5) + {(+87,5) + [(+3,8) + (-0,8)]}

= [(-87,5) + (+87,5)] + [(+3,8) + (-0,8)]

= 0 + 3 = 3

C = [(+9,5) + (-13)] + [(-5) + (8,5)]

= [(+9,5) + (+8,5)] + [(-5) + (-13)]

= 18 + (-18) = 0

A = ( -5,85 )  + ( 41,3 +5 )

     =( -5,85 +5 ) + 41,3 = -0,85 + 41,3 = 40,45

B = ( -87,5 ) + { 87,5 + [ 3,8 +( -0,8) ]

    = [ ( -87,5 )+ 87,5 ] + [ 3,8 + ( -0,8) ]

     =0 + 3 = 3

  C=[ 9,5 + ( -13) ] + [ (-5) +8,5 ]

      =9,5 + ( -13 ) + ( -5 ) + 8,5

       = ( 9,5 +8,5 ) + [ ( -13) + (-5)]

        =18 + ( -18 ) =0

Bài 1: 

a: A=-5,85+41,3-5=41,3-10,85=30,45

b: B=-87,5+87,5+3,8-0,8=3

c: C=9,5-13-5+8,5=18-18=0

\(A=\left(-5,85\right)+\left\{\left[\left(+41,3\right)+\left(+5\right)\right]+\left(+0,85\right)\right\}\)

\(A=\left(-5,85\right)+\left\{\left[41,3+5\right]+0,85\right\}\)

\(A=\left(-5,85\right)+\left\{41,3+5+0,85\right\}\)

\(A=\left(-5,85\right)+\left\{41,3+5,85\right\}\)

\(A=\left(-5,85\right)+41,3+5,85\)

\(A=\left(-5,85\right)+5,85+41,3\)

\(A=0+41,3\)

\(A=41,3\)

\(B=\left(-87,5\right)+\left\{\left(+87,5\right)+\left[\left(+3,8\right)+\left(-0,8\right)\right]\right\}\)

\(B=\left(-87,5\right)+87,5+3,8+\left(-0,8\right)\)

\(B=\left[\left(-87,5\right)+87,5\right]+\left[3,8+\left(-0,8\right)\right]\)

\(B=0+3\)

\(B=3\)

\(C=\left[\left(+9,8\right)+\left(-13\right)\right]+\left[\left(-5\right)+\left(+8,5\right)\right]\)

\(C=\left(-3,2\right)+3,5\)

\(C=0,3\)

A = (-5,85) + {[(+41,3)+(+5) + (+0,85))}

= {(-5,85) + [(+5) + (0,85)]} + (+ 41,3)

= {(-5,85) + (5,85)} + (+ 41,3)

= 0 + 41,3

= 41,3

B = (-87,5) + {(+87,5) + [(+3,8) + (-0,8)]}

= [(-87,5) + (+87,5)] + [(+3,8) + (-0,8)]

= 0 + 3 = 3

C = [(+9,5) + (-13)] + [(-5) + (8,5)]

= [(+9,5) + (+8,5)] + [(-5) + (-13)]

= 18 + (-18) = 0

A = (-5,85) + {[(+41,3)+(+5) + (+0,85))}

= {(-5,85) + [(+5) + (0,85)]} + (41,3)

= {(-5,85) + (5,85)} + (41,3)

= 41,3

B = (-87,5) + {(+87,5) + [(+3,8) + (-0,8)]}

= [(-87,5) + (+87,5)] + [(+3,8) + (-0,8)]

= 0 + 3 = 3

C = [(+9,5) + (-13)] + [(-5) + (8,5)]

= [(+9,5) + (+8,5)] + [(-5) + (-13)]

= 18 + (-18) = 0

HT

A = (-5,85) + {[(+41,3)+(+5) + (+0,85))}

= {(-5,85) + [(+5) + (0,85)]} + (41,3)

= {(-5,85) + (5,85)} + (41,3)

= 41,3

B = (-87,5) + {(+87,5) + [(+3,8) + (-0,8)]}

= [(-87,5) + (+87,5)] + [(+3,8) + (-0,8)]

= 0 + 3 = 3

C = [(+9,5) + (-13)] + [(-5) + (8,5)]

= [(+9,5) + (+8,5)] + [(-5) + (-13)]

= 18 + (-18) = 0

a)\(\frac{7}{3}.\left( { - 2,5} \right).\frac{6}{7} = \frac{7}{3}.\frac{6}{7}.\left( { - 2,5} \right) = 2.\left( { - 2,5} \right) =  - 5\)

b)

\(\begin{array}{l}0,8.\frac{{ - 2}}{9} - \frac{4}{5}.\frac{7}{9} - 0,2\\ = \frac{4}{5}.\frac{{ - 2}}{9} - \frac{4}{5}.\frac{7}{9}-\frac{2}{10}\\ = \frac{4}{5}.\left( {\frac{{ - 2}}{9} - \frac{7}{9}} \right) -\frac{1}{5}\\ = \frac{4}{5}.\left( { - 1} \right)-\frac{1}{5} \\= \frac{{ - 4}}{5}-\frac{1}{5}\\=\frac{-5}{5}\\=-1.\end{array}\)

a)

 \(\begin{array}{l}\left( { - \frac{5}{6}} \right) - \left( { - 1,8} \right) + \left( { - \frac{1}{6}} \right) - 0,8\\ = \left( { - \frac{5}{6}} \right) + 1,8 + \left( { - \frac{1}{6}} \right) - 0,8\\ = \left[ {\left( { - \frac{5}{6}} \right) + \left( { - \frac{1}{6}} \right)} \right] + \left[ {1,8 - 0,8} \right]\\ =\frac{-6}{6}+1=  - 1 + 1 = 0\end{array}\)

b)

 \(\begin{array}{l}\left( { - \frac{9}{7}} \right) + \left( { - 1,23} \right) - \left( { - \frac{2}{7}} \right) - 0,77\\ = \left[ {\left( { - \frac{9}{7}} \right) - \left( { - \frac{2}{7}} \right)} \right] + \left[ {\left( { - 1,23} \right) - 0,77} \right]\\ =\frac{-7}{7}+(-2)=  - 1 + \left( { - 2} \right) =  - 3\end{array}\)

a)

\(\begin{array}{l}1,8 - \left( {\frac{3}{7} - 0,2} \right)\\ = 1,8 - \frac{3}{7} + 0,2\\ = \left( {1,8 + 0,2} \right) - \frac{3}{7}\\ = 2 - \frac{3}{7} =\frac{{14}}{7}-\frac{{3}}{7}= \frac{{11}}{7}\end{array}\)

b)

\(\begin{array}{l}12,5 - \frac{{16}}{{13}} + \frac{3}{{13}}\\ = 12,5 - \frac{{16}}{{13}} + \frac{3}{{13}}\\ = 12,5 + \left( { - \frac{{16}}{{13}} + \frac{3}{{13}}} \right)\\ = 12,5 + \left( { - 1} \right) = 11,5\end{array}\)