\(a.\dfrac{3}{5}-\dfrac{-7}{10}-\dfrac{13}{-20}=\dfrac{12}{20}-\dfrac{-14}{20}-\dfrac{-13}{20}=\dfrac{12-\left(-14\right)-\left(-13\right)}{20}=\dfrac{39}{20}\)

\(b.\dfrac{3}{4}+\dfrac{-1}{3}-\dfrac{5}{18}=\dfrac{3}{4}+\left(\dfrac{-6}{18}-\dfrac{5}{18}\right)=\dfrac{3}{4}+\dfrac{-11}{18}=\dfrac{27}{36}-\dfrac{-22}{36}=\dfrac{49}{36}\)

\(c.\dfrac{3}{13}-\dfrac{5}{-8}+\dfrac{-1}{2}=\dfrac{3}{13}-\left(\dfrac{5}{-8}+\dfrac{-4}{8}\right)=\dfrac{3}{13}-\dfrac{1}{8}=\dfrac{24}{104}-\dfrac{13}{104}=\dfrac{11}{104}\)

\(d.\dfrac{1}{2}+\dfrac{1}{-3}=\dfrac{3}{6}+\dfrac{-2}{6}=\dfrac{1}{6}\)

\(a,\dfrac{3}{5}-\dfrac{-7}{10}-\dfrac{13}{-20}\)

\(=\dfrac{12}{20}+\dfrac{14}{20}+\dfrac{13}{20}\)

\(=\dfrac{12+14+13}{20}\)

\(=\dfrac{39}{20}\)

\(b,\dfrac{3}{4}+\dfrac{-1}{3}-\dfrac{5}{18}\)

\(=\dfrac{27}{36}+\dfrac{-12}{36}-\dfrac{10}{36}\)

\(=\dfrac{27+\left(-12\right)-10}{36}\)

\(=\dfrac{5}{36}\)

\(c,\dfrac{3}{13}-\dfrac{5}{-8}+\dfrac{-1}{2}\)

\(=\dfrac{24}{104}-\dfrac{-65}{104}+\dfrac{-52}{104}\)

\(=\dfrac{24-\left(-65\right)+\left(-52\right)}{104}\)

\(=\dfrac{37}{104}\)

\(d,\dfrac{1}{2}+\dfrac{1}{-3}\)

\(=\dfrac{3}{6}+\dfrac{-2}{6}\)

\(=\dfrac{3+\left(-2\right)}{6}\)

\(=\dfrac{1}{6}\)

mình ghi nhầm nên các bạn cứ hết hai phân số là một câu nhé ví dụ như \(\dfrac{-5}{8}\):\(\dfrac{15}{4}\)

Giải:

a) \(A=\dfrac{5}{13}.\dfrac{5}{7}+\dfrac{-20}{41}+\dfrac{5}{13}+\dfrac{-21}{41}\)

\(\Leftrightarrow A=\dfrac{5}{13}.\dfrac{5}{7}+\dfrac{5}{13}+\dfrac{-21}{41}+\dfrac{-20}{41}\)

\(\Leftrightarrow A=\dfrac{5}{13}\left(\dfrac{5}{7}+1\right)+\dfrac{-41}{41}\)

\(\Leftrightarrow A=\dfrac{5}{13}.\dfrac{12}{7}+\left(-1\right)\)

\(\Leftrightarrow A=\dfrac{60}{91}+\left(-1\right)=-\dfrac{31}{91}\)

Vậy ...

b) \(B=\dfrac{5}{7}.\dfrac{2}{11}+\dfrac{5}{7}.\dfrac{12}{11}-\dfrac{5}{7}.\dfrac{7}{11}\)

\(\Leftrightarrow B=\dfrac{5}{7}\left(\dfrac{2}{11}+\dfrac{12}{11}-\dfrac{7}{11}\right)\)

\(\Leftrightarrow B=\dfrac{5}{7}.\dfrac{7}{11}\)

\(\Leftrightarrow B=\dfrac{5}{11}\)

Vậy ...

c) \(C=\dfrac{-2}{3}+\dfrac{-5}{7}+\dfrac{2}{3}+\dfrac{-2}{7}\)

\(\Leftrightarrow C=\left(\dfrac{-2}{3}+\dfrac{2}{3}\right)+\left(\dfrac{-2}{7}+\dfrac{-5}{7}\right)\)

\(\Leftrightarrow C=0+\left(-1\right)=-1\)

Vậy ...

A

a: \(=\dfrac{4\cdot2+4\cdot9}{55}+\dfrac{5}{6}=\dfrac{4}{5}+\dfrac{5}{6}=\dfrac{49}{30}\)

b: \(=\dfrac{3}{2}\cdot\dfrac{3}{5}-\left(\dfrac{3}{7}+\dfrac{3}{20}\right)\cdot\dfrac{10}{3}\)

\(=\dfrac{9}{10}-\dfrac{81}{140}\cdot\dfrac{10}{3}\)

\(=\dfrac{9}{10}-\dfrac{27}{14}=\dfrac{-36}{35}\)

c: \(=15+\dfrac{3}{13}-3-\dfrac{4}{7}-8-\dfrac{3}{13}\)

\(=4-\dfrac{4}{7}=\dfrac{24}{7}\)

d: \(=\dfrac{-7}{9}\left(\dfrac{4}{11}+\dfrac{7}{11}\right)+5+\dfrac{7}{9}=5\)

\(A=\dfrac{-3}{5}.\dfrac{3}{13}+\dfrac{-3}{5}.\dfrac{10}{13}+5\)

\(A=\dfrac{-3}{5}\left(\dfrac{3}{13}+\dfrac{10}{13}\right)+5\)

\(A=\dfrac{-3}{5}.1+5\)

\(A=\dfrac{-3}{5}+5\)

\(A=\dfrac{22}{5}\)

cảm ơn bạn nha, làm giúp mk câu b đc ko?

a, \(\left(2\dfrac{3}{5}-3\dfrac{5}{9}\right):\left(3\dfrac{10}{21}-1\dfrac{3}{7}\right)\)

\(=\dfrac{-43}{45}:\dfrac{43}{21}=\dfrac{-43}{45}.\dfrac{21}{43}=\dfrac{-7}{15}\)

b, \(5\dfrac{1}{2}-14\dfrac{3}{7}:\dfrac{9}{13}-3\dfrac{4}{7}:\dfrac{9}{13}\)

\(=5\dfrac{1}{2}-14\dfrac{3}{7}.\dfrac{13}{9}-3\dfrac{4}{7}.\dfrac{13}{9}\)

\(=5\dfrac{1}{2}-\dfrac{13}{9}.\left(14\dfrac{3}{7}+\dfrac{4}{7}\right)\)

\(=5\dfrac{1}{2}-\dfrac{13}{9}.15=5\dfrac{1}{2}-\dfrac{65}{3}\)

\(=\dfrac{-97}{6}\)

Chúc bạn học tốt!!!

b, \(5\dfrac{1}{2}-14\dfrac{3}{7}:\dfrac{9}{13}-3\dfrac{4}{7}:\dfrac{9}{13}\)

\(=5\dfrac{1}{2}-\dfrac{13}{9}.\left(14\dfrac{3}{7}+3\dfrac{4}{7}\right)\)

\(=5\dfrac{1}{2}-\dfrac{13}{9}.18=5\dfrac{1}{2}-26\)

\(=\dfrac{-41}{2}\)

Chúc bạn học tốt!!!

\(a.-8:\left(4\dfrac{1}{5}x+\dfrac{3}{10}\right)=4\dfrac{4}{9}\)

\(4\dfrac{1}{5}x+\dfrac{3}{10}=\left(-8\right):4\dfrac{4}{9}\)

\(4\dfrac{1}{5}x+\dfrac{3}{10}=\dfrac{-9}{5}\)

\(4\dfrac{1}{5}x=\dfrac{-9}{5}-\dfrac{3}{10}\)

\(4\dfrac{1}{5}x=\dfrac{-21}{10}\)

\(x=\dfrac{-21}{10}:\dfrac{21}{5}\)

\(x=\dfrac{-1}{2}\)

Vay \(x=\dfrac{-1}{2}\).

\(b.4\dfrac{2}{3}-\left(\dfrac{3}{5}:x\right)=-20\%\)

\(\dfrac{14}{3}-\left(\dfrac{3}{5}:x\right)=\dfrac{-1}{5}\)

\(\dfrac{3}{5}:x=\dfrac{14}{3}-\dfrac{-1}{5}\)

\(\dfrac{3}{5}:x=\dfrac{73}{15}\)

\(x=\dfrac{3}{5}:\dfrac{73}{15}\)

\(x=\dfrac{9}{73}\)

Vay \(x=\dfrac{9}{73}\).

Câu c; d; e tương tự nhé.

2) Tinh nhanh:

a) \(\dfrac{5}{23}\) . \(\dfrac{17}{26}\) + \(\dfrac{5}{23}\) . \(\dfrac{10}{26}\) - \(\dfrac{5}{23}\)

= \(\dfrac{5}{23}\) . \(\left(\dfrac{17}{26}+\dfrac{10}{26}-1\right)\)

= \(\dfrac{5}{23}\) . \(\left(\dfrac{27}{26}-1\right)\) = \(\dfrac{5}{23}\) . \(\dfrac{1}{26}\)

= \(\dfrac{5}{598}\)

b) \(\dfrac{1}{7}.\dfrac{5}{9}+\dfrac{5}{9}.\dfrac{2}{7}+\dfrac{5}{9}.\dfrac{1}{7}+\dfrac{5}{9}.\dfrac{3}{7}\)

= \(\dfrac{5}{9}.\left(\dfrac{1}{7}+\dfrac{2}{7}+\dfrac{1}{7}+\dfrac{3}{7}\right)\)

= \(\dfrac{5}{9}\) . 1= \(\dfrac{5}{9}\)