a) Ta có: \(\dfrac{-11}{15}< \dfrac{x}{15}< \dfrac{-8}{15}\)

nên -11<x<-8

hay \(x\in\left\{-10;-9\right\}\)

b) Ta có: \(\dfrac{3}{7}< \dfrac{x}{21}< \dfrac{2}{3}\)

\(\Leftrightarrow\dfrac{9}{21}< \dfrac{x}{21}< \dfrac{14}{21}\)

Suy ra: 9<x<14

hay \(x\in\left\{10;11;12;13\right\}\)

c) Ta có: \(\dfrac{-67}{21}< \dfrac{x}{168}< \dfrac{-3}{8}\)

nên \(\dfrac{-536}{168}< \dfrac{x}{168}< \dfrac{-63}{168}\)

Suy ra: -536<x<-63

hay \(x\in\left\{-535;-534;...;-64\right\}\)

a \(\dfrac{6}{15}+\dfrac{11}{15}=\dfrac{17}{15}\)

b \(\dfrac{22}{77}-\dfrac{14}{77}=\dfrac{8}{77}\)

c \(\dfrac{11}{13}\times\dfrac{26}{31}=11\times\dfrac{2}{31}=\dfrac{22}{31}\)

d \(\dfrac{1}{2}\times3\times\dfrac{2}{5}=\dfrac{3}{5}\)

a, 2/5 + 11/15 = 6/15 + 11/15 = 17/15

b,2/7 - 2/11 = 22/77 - 14/77 = 8/77

c, 11/13 x 26/31= 11 x 2/31 =22/31

d, 1/2 : 1/3 x 2/5

=  ( 1/2 x 2/5 ) : 1/3

=     1/5        : 1/3

=         3/5

a: \(A=\dfrac{-7}{28}\cdot\dfrac{15}{25}=\dfrac{-1}{4}\cdot\dfrac{3}{5}=\dfrac{-3}{20}\)

b: \(B=\dfrac{-5\cdot7}{14\cdot\left(-3\right)}=\dfrac{35}{42}=\dfrac{5}{6}\)

c: \(C=\dfrac{-1}{5}-\dfrac{1}{5}\cdot\dfrac{3}{5}=\dfrac{-1}{5}-\dfrac{3}{25}=\dfrac{-8}{25}\)

d: \(D=\dfrac{-3}{4}-\dfrac{1}{4}=-1\)

e: \(E=\dfrac{-4}{5}\left(1-\dfrac{15}{16}\right)=\dfrac{-4}{5}\cdot\dfrac{1}{16}=\dfrac{-1}{20}\)

f: \(F=\dfrac{6-7}{4}\cdot\dfrac{4+12}{22}=\dfrac{-1}{4}\cdot\dfrac{8}{11}=\dfrac{-2}{11}\)

\(\Rightarrow\left(x+2\right)\left(\dfrac{1}{9}+\dfrac{1}{11}-\dfrac{1}{13}-\dfrac{1}{15}\right)=0\\ \Rightarrow x=2\left(\dfrac{1}{9}+\dfrac{1}{11}-\dfrac{1}{13}-\dfrac{1}{15}\ne0\right)\)

help 

\(a,\dfrac{5}{13}\times\dfrac{4}{15}\times13=\dfrac{5\times4\times13}{13\times5\times3}=\dfrac{4}{3}\\ b,\left(\dfrac{3}{7}+\dfrac{5}{2}\right)\times\dfrac{7}{5}=\dfrac{3}{7}\times\dfrac{7}{5}+\dfrac{5}{2}\times\dfrac{7}{5}=\dfrac{3}{5}+\dfrac{7}{2}=\dfrac{6}{10}+\dfrac{35}{10}=\dfrac{41}{10}\\ c,\dfrac{1}{5}\times\dfrac{11}{18}+\dfrac{11}{18}\times\dfrac{3}{5}=\dfrac{11}{18}\times\left(\dfrac{1}{5}+\dfrac{3}{5}\right)=\dfrac{11}{18}\times\dfrac{4}{5}=\dfrac{22}{45}\)

a, 4/3  b, 41/10   c,22/45

=>11/10x=11/15

hay x=2/3

\(\dfrac{3x}{5}+\dfrac{x}{2}=\dfrac{11}{15}\Rightarrow18x+15x=22\Leftrightarrow33x=22\Leftrightarrow x=\dfrac{2}{3}\)

\(\Leftrightarrow x\cdot\dfrac{11}{10}=\dfrac{11}{15}\)

hay x=2/3

\(\dfrac{3}{5}x+\dfrac{1}{2}x=\dfrac{11}{15}\)

\(\Leftrightarrow\)\(\dfrac{11}{10}x=\dfrac{11}{15}\)

\(\Leftrightarrow\)\(x=\dfrac{2}{3}\)

\(x\times\dfrac{3}{5}+x\times\dfrac{1}{2}=\dfrac{11}{15}\)

\(x\times\left(\dfrac{3}{5}+\dfrac{1}{2}\right)=\dfrac{11}{15}\)

\(x\times\dfrac{11}{10}=\dfrac{11}{15}\)

\(x=\dfrac{11}{15}\div\dfrac{11}{10}\)

\(x=\dfrac{2}{3}\)

\(x\div\dfrac{15}{11}=\dfrac{-3}{12}\div8\)

\(x\div\dfrac{15}{11}=-\dfrac{1}{32}\)

\(x=-\dfrac{1}{32}\cdot\dfrac{15}{11}\)

\(x=-\dfrac{15}{352}\)