\(\dfrac{-5}{7}+\dfrac{3}{4}+\dfrac{-1}{5}+\dfrac{-2}{7}+\dfrac{1}{4}\\ =\left(\dfrac{-5}{7}+\dfrac{-2}{7}\right)+\left(\dfrac{3}{4}+\dfrac{1}{4}\right)-\dfrac{1}{5}\\ =-1+1-\dfrac{1}{5}\\ =0-\dfrac{1}{5}\\ =\dfrac{-1}{5}\)

\(\left(\dfrac{-1}{6}+\dfrac{5}{12}\right)+\dfrac{7}{12}\\ =\dfrac{-1}{6}+\dfrac{5}{12}+\dfrac{7}{12}\\ =\dfrac{-1}{6}+1\\ =\dfrac{5}{6}\)

Các phân số bằng 3/4 là:

\(\dfrac{45}{60};\dfrac{12}{16}\)

sao ko có dữ kiện gì về z vậy

\(\dfrac{50}{70}=\dfrac{5}{7}\\ \dfrac{24}{120}=\dfrac{1}{5}\)

\(c,C=\dfrac{-7}{10}.\dfrac{4}{13}+\dfrac{-7}{10}.\dfrac{9}{13}+1\dfrac{7}{10}\\ =\dfrac{-7}{10}.\left(\dfrac{4}{13}+\dfrac{9}{13}\right)+\dfrac{17}{10}\\ =\dfrac{-7}{10}.1+\dfrac{17}{10}\\ =\dfrac{-7}{10}+\dfrac{17}{10}\\ =1\\ d,D=0,7.2\dfrac{2}{3}.20.0,375.\dfrac{5}{28}\\ =14.\dfrac{8}{3}.\dfrac{15}{224}\\ =\dfrac{112}{3}.\dfrac{15}{224}\\ =\dfrac{5}{2}\)

\(a,A=13\dfrac{2}{11}-\left(2\dfrac{3}{4}+9\dfrac{2}{11}\right)\\ =\dfrac{145}{11}-\left(\dfrac{11}{4}+\dfrac{101}{11}\right)\\ =\dfrac{145}{11}-\dfrac{525}{44}\\ =\dfrac{5}{4}\\ b,B=\left(7\dfrac{5}{9}+3\dfrac{7}{13}\right)-5\dfrac{5}{9}\\ =\left(\dfrac{68}{9}+\dfrac{46}{13}\right)-\dfrac{50}{9}\\ =\dfrac{1298}{117}-\dfrac{50}{9}\\ =\dfrac{72}{13}\)

xem lại nhé

\(\dfrac{4}{25}\times\dfrac{3}{5}=\dfrac{12}{125}\)

\(\dfrac{2}{7}:\dfrac{3}{4}=\dfrac{2}{7}\times\dfrac{4}{3}=\dfrac{8}{21}\)