(-12) + 25 + 75 + 12 = (-12) + 12 + 25 + 75 = 0 +100 = 100

a) (-12) + 25 + 75 + 12 = (-12) + 12 + 25 + 75 = 0 +100 = 100.

b) 60 +12 + (-17) + (-43) = 60 + [(-47) + (-43)] +12.

c) (-2) + (-87) + (-18) + 87 = [(-2) + (-18)] + [(-87) + 87].

d) (-1)+(-2) + 36 + (-17) = 36+[(-1) + (-2) + (-17)].

a, (-12) + 25 + 75 + 12

= [ (-12) + 12] + (25 + 75)

= 0 + 100

= 100

b, 60 + 12 + (-17) + (-43)

= -(17 + 43) + 60 + 12

= - 60 + 60  + 12

= 0 + 12

= 12

a) (12 + 8) x 4 = 20 x 4

                         = 80

12 + 8 x 4 = 12 + 32

                         = 44

b) 25 + 75 : 5 = 25 + 15

                         = 40

(25 + 75) : 5 = 100 : 5

                         = 20

a, \(\dfrac{7}{15}\)+\(\dfrac{18}{54}\)
=  \(\dfrac{7}{15}\)+ \(\dfrac{1}{3}\)
=  \(\dfrac{7}{15}\)+\(\dfrac{5}{15}\)
=    \(\dfrac{12}{15}\) = \(\dfrac{4}{5}\) =0,8
b, \(\dfrac{12}{25}\)+\(\dfrac{23}{75}\)-\(\dfrac{1}{4}\)
=     \(\dfrac{59}{75}\)   -\(\dfrac{1}{4}\)
=         \(\dfrac{161}{300}\)
   

a, 7/15 + 18/54 = 4/5

a)27.75+25.27-150

=27.(75+25)-150

=27.100-150

=2700-150

=2550

\(a,27.75+25.27-150\)

\(=27.\left(75+25\right)-150\)

\(=27.100-150\)

\(=2700-150\)

\(=2550\)

\(b,12:\left\{390:\left[500-\left(125+35.7\right)\right]\right\}\)

\(=12:\left\{390:\left[500-\left(125+245\right)\right]\right\}\)

\(=12:\left[390:\left(500-370\right)\right]\)

\(=12:\left(390:130\right)\)

\(=12:3\)

\(=4\)

a) \(27\cdot75+25\cdot27-150\)

\(=27\cdot100-150\)

\(=2700-150\)

\(=2550\)

b) \(12\div\left\{390\div\left[500-\left(125+35\cdot7\right)\right]\right\}\)

\(=12\div\left\{390\div\left[500-370\right]\right\}\)

\(=12\div\left(390\div130\right)\)

\(=12\div3\)

\(=4\)

a) 27 . 75 + 25 . 27 - 150 = 2025 + 675 - 150 = 2700 - 150 = 2550.

Lưu ý. Có thể dùng tính chất phân phối của phép nhân đối với phép cộng để nhẩm:

27 . 75 + 25 . 27 - 150 = 27 . (75 + 25) - 150 = 27 . 100 - 150 = 2700 - 150 = 2550.

b) 12 : {390 : [500 - (125 + 35 . 7)]} = 12 : {390 : [500 - (125 + 245)]}

= 12 : [390 : (500 - 370)] = 12 : (390 : 130) = 12 : 3 = 4.

a,27+75.25+27-150

= 27.(75+25)-150

=27.100-150

=2700-150

=2550

b,12:{390:[500-(125+35.7)]}

=12:{390:[500-(125+245)]}

=12:{390:[500-370]}

=12:{390:130}

=12:3

=4

Thank you very much

a)\(27.75+25.27-150=27\left(75+25\right)-150\)

\(=27.100-150\)

\(=2700-150\)

\(=2550\)

b)\(12:\left\{390:\left[500-\left(125+35.7\right)\right]\right\}=12:\left\{390:\left[500-\left(125+245\right)\right]\right\}\)

\(=12:\left[390:\left(500-370\right)\right]\)

\(=12:\left(390:130\right)\)

\(=12:3\)

=4