a, [ 545 - ( 45 + 4 x 25 ) ] : 50 - 2000 : 250

 [545 -( 45 + 100) ] : 50 - 2000 : 250

[ 545 - 145 ] : 50 - 2000 : 250

400 : 50 - 2000 : 250 

8 - 8 = 0

b, [ 504 - ( 25 x 8 + 70 ) ] : 9 - 15 + 19

[ 504 - ( 200 + 70 ) ] : 9 - 15 + 19

[ 504 - 270 ] : 9 - 15 + 19 

234 : 9 - 15 + 19

26 - 15 + 19 = 30

c, 5 x { 26 - [ 3 x ( 5 + 2 x 5 ) + 15 ] : 15 }

5 x { 26 -[ 3 x ( 5 + 10 ) + 15 ] : 15 } 

5 x { 26 - [ 3 x 15 + 15 ] : 15 } 

5 x {  26 - [ 45 + 15 ] : 15 } 

5 x { 26 - 60 : 15 } 

5 x { 26 - 4 } 

5 x 22 = 110

\(\left(\dfrac{6}{7}+\dfrac{3}{14}\right):\dfrac{3}{7}\times\dfrac{1}{70}\)

\(=\left(\dfrac{12}{14}+\dfrac{3}{14}\right):\dfrac{3}{7}\times\dfrac{1}{70}\)

\(=\dfrac{15}{14}:\dfrac{3}{7}\times\dfrac{1}{70}\)

\(=\dfrac{15}{14}\times\dfrac{7}{3}\times\dfrac{1}{70}\)

\(=\dfrac{15\times7\times1}{14\times3\times70}\)

\(=\dfrac{105}{2940}=\dfrac{1}{28}\)

\(\left(\dfrac{6}{7}+\dfrac{3}{14}\right):\dfrac{3}{7}\times\dfrac{1}{70}\)

\(=\left(\dfrac{12}{14}+\dfrac{3}{14}\right)\times\dfrac{7}{3}\times\dfrac{1}{70}\)

\(=\dfrac{15}{14}\times\dfrac{1}{30}\)

\(=\dfrac{1}{28}\)

{65; 56; 5}

{350; 980; 50; 140}

{75; 84; 15; 24}

đầy đủ phần ngoặc hay gì đó

\(\dfrac{11}{2}\): \(\dfrac{1}{4}\) \(\times\) \(\dfrac{5}{3}\)

= \(\dfrac{11}{2}\) \(\times\) \(\dfrac{4}{1}\) \(\times\) \(\dfrac{5}{3}\)

= 22 \(\times\) \(\dfrac{5}{3}\)

= \(\dfrac{110}{3}\)

\(\dfrac{5}{2}-\dfrac{1}{4}+\dfrac{5}{3}\)

= \(\dfrac{30}{12}-\dfrac{3}{12}+\dfrac{20}{12}\)

= \(\dfrac{7}{12}\) 

\(\dfrac{14}{5}\times\dfrac{2}{3}\)+ 5

= \(\dfrac{28}{15}\) + 5

= \(\dfrac{28}{15}\) + \(\dfrac{75}{15}\)

= \(\dfrac{103}{15}\)