1.
\(a,\dfrac{2}{3}+\dfrac{1}{5}\cdot\dfrac{10}{7}\)
\(=\dfrac{2}{3}+\dfrac{2}{7}\)
\(=\dfrac{14}{21}+\dfrac{6}{21}\)
\(=\dfrac{20}{21}\)
\(b,\dfrac{7}{12}-\dfrac{27}{7}\cdot\dfrac{1}{18}\)
\(=\dfrac{7}{12}-\dfrac{3}{7}\cdot\dfrac{1}{2}\)
\(=\dfrac{7}{12}-\dfrac{3}{14}\)
\(=\dfrac{31}{84}\)
\(c,\dfrac{3}{10}\cdot\dfrac{-5}{6}-\dfrac{1}{8}\)
\(=\dfrac{1}{2}\cdot\dfrac{-1}{2}-\dfrac{1}{8}\)
`= -1/4 - 1/8`
`= -2/8 - 1/8`
`= -3/8`
\(d,-\dfrac{4}{9}:\dfrac{8}{3}+\dfrac{1}{18}\)
`= -4/9 * 3/8 + 1/18`
`= -1/3 * 1/2 + 1/18`
`= -1/6 + 1/18`
`= -3/18 + 1/18`
`= -2/18 = -1/9`
\(e,\left\{\left[\left(\dfrac{1}{2}-\dfrac{2}{3}\right)^2:2\right]-1\right\}\cdot\dfrac{4}{5}\)
\(=\left\{\left[\left(\dfrac{3}{6}-\dfrac{4}{6}\right)^2:2\right]-1\right\}\cdot\dfrac{4}{5}\)
\(=\left\{\left[\left(-\dfrac{1}{6}\right)^2:2\right]-1\right\}\cdot\dfrac{4}{5}\)
\(=\left\{\left[\dfrac{1}{36}:2\right]-1\right\}\cdot\dfrac{4}{5}\)
\(=\left\{\dfrac{1}{72}-1\right\}\cdot\dfrac{4}{5}\)
`= (-71/72) * 4/5`
`= -71/90`
\(g,\left[\left(\dfrac{32}{25}+1\right):\dfrac{2}{3}\right]\cdot\left(\dfrac{3}{4}-\dfrac{1}{8}\right)^2\)
\(=\left[\left(\dfrac{32}{25}+\dfrac{25}{25}\right):\dfrac{2}{3}\right]\cdot\left(\dfrac{6}{8}-\dfrac{1}{8}\right)^2\)
\(=\left[\dfrac{57}{25}:\dfrac{2}{3}\right]\cdot\left(\dfrac{5}{8}\right)^2\)
\(=\dfrac{171}{50}\cdot\dfrac{25}{64}\)
\(=\dfrac{171}{128}\)
2.
\(a,\dfrac{1}{7}\cdot\dfrac{1}{5}+\dfrac{1}{7}\cdot\dfrac{2}{5}+\dfrac{1}{7}\cdot\dfrac{4}{5}\)
\(=\dfrac{1}{7}\cdot\left(\dfrac{1}{5}+\dfrac{2}{5}+\dfrac{4}{5}\right)\)
\(=\dfrac{1}{7}\cdot\dfrac{7}{5}\)
\(=\dfrac{1}{5}\)
\(b,\dfrac{4}{9}\cdot\dfrac{-1}{19}+\dfrac{5}{9}\cdot\dfrac{-1}{19}\)
\(=\left(\dfrac{4}{9}+\dfrac{5}{9}\right)\cdot\dfrac{-1}{19}\)
\(=1\cdot\dfrac{-1}{19}\)
\(=\dfrac{-1}{19}\)
\(c,\dfrac{8}{19}\cdot\dfrac{5}{11}+\dfrac{7}{11}\cdot\dfrac{8}{19}-\dfrac{1}{11}\cdot\dfrac{8}{19}\)
\(=\left(\dfrac{5}{11}+\dfrac{7}{11}-\dfrac{1}{11}\right)\cdot\dfrac{8}{19}\)
\(=1\cdot\dfrac{8}{9}=\dfrac{8}{9}\)
\(d,\left(\dfrac{17}{28}+\dfrac{18}{29}-\dfrac{19}{30}-\dfrac{20}{31}\right)\cdot\left(\dfrac{-5}{12}+\dfrac{1}{4}+\dfrac{1}{6}\right)\)
\(=\left(\dfrac{17}{28}+\dfrac{18}{29}-\dfrac{19}{30}-\dfrac{20}{31}\right)\cdot\left(\dfrac{-5}{12}+\dfrac{3}{12}+\dfrac{2}{12}\right)\)
\(=\left(\dfrac{17}{28}+\dfrac{18}{29}-\dfrac{19}{30}-\dfrac{20}{31}\right)\cdot\left(\dfrac{-5+3+2}{12}\right)\)
\(=\left(\dfrac{17}{28}+\dfrac{18}{29}-\dfrac{19}{30}-\dfrac{20}{31}\right)\cdot0=0\)
\(e,\dfrac{5\cdot18-10\cdot27+15\cdot36}{10\cdot36-20\cdot54+30\cdot72}\)
\(=\dfrac{5\cdot2\cdot9-10\cdot3\cdot9+15\cdot4\cdot9}{10\cdot4\cdot9-20\cdot9\cdot6+30\cdot9\cdot8}\)
\(=\dfrac{10\cdot9-30\cdot9+60\cdot9}{40\cdot9-120\cdot9+240\cdot9}\)
\(=\dfrac{\left(10-30+60\right)\cdot9}{\left(40-120+240\right)\cdot9}\)
\(=\dfrac{40\cdot9}{160\cdot9}=\dfrac{1\cdot1}{4\cdot1}=\dfrac{1}{4}\)
3.
\(a,\dfrac{2}{3}-4x=\dfrac{1}{2}-\dfrac{2}{5}\)
\(\Rightarrow\dfrac{2}{3}-4x=\dfrac{1}{10}\)
\(\Rightarrow4x=\dfrac{2}{3}-\dfrac{1}{10}\)
\(\Rightarrow4x=\dfrac{17}{30}\)
\(\Rightarrow x=\dfrac{17}{30}:4\)
\(\Rightarrow x=\dfrac{17}{120}\)
Vậy `x = 17/120`
\(b,\dfrac{1}{2}+\dfrac{2}{3}:x=\dfrac{-5}{4}\)
\(\Rightarrow\dfrac{2}{3}:x=\dfrac{-5}{4}-\dfrac{1}{2}\)
\(\Rightarrow\dfrac{2}{3}:x=-\dfrac{7}{4}\)
`=> x = 2/3 : -7/4`
`=> x = -8/21`
Vậy `x = -8/21`
`c.` Mình ko biết làm ạ!
\(d.3,8:2x=\dfrac{1}{4}:2\dfrac{2}{3}\)
`=> 3,8 : 2x = 1/4 : 8/3`
`=> 3,8 : 2x =3/32`
`=> 1,9x = 3/32`
`=> x = 3/32 : 1,9`
`=> x = 15/304`
Vậy `x = 15/304`
\(e,1\dfrac{7}{9}:\left[\left(1-x\right):\dfrac{2}{3}+\left(\dfrac{1}{2}\right)^2\cdot\dfrac{4}{5}\right]=\dfrac{5}{9}\)
\(\Rightarrow\dfrac{16}{9}:\left[\left(1-x\right):\dfrac{2}{3}+\dfrac{1}{4}\cdot\dfrac{4}{5}\right]=\dfrac{5}{9}\)
`=> (1 - x) : 2/3 + 1/4 * 4/5 = 16/9 : 5/9`
`=> (1 - x) : 2/3 + 1/5 = 16/5`
`=> (1 - x) : 2/3 = 16/5 - 1/5`
`=> (1 - x) : 2/3 = 3`
`=> 1 - x = 3 * 2/3`
`=> 1 - x = 2`
`=> x = 1 - 2`
`=> x = -1`
Vậy `x = -1`
4.
a, Mình không biết làm ạ!
\(b,\dfrac{\dfrac{1}{9}-\dfrac{1}{7}-\dfrac{1}{11}}{\dfrac{4}{9}-\dfrac{4}{7}-\dfrac{4}{11}}+\dfrac{\dfrac{3}{5}-\dfrac{3}{25}-\dfrac{3}{125}-\dfrac{3}{625}}{\dfrac{4}{5}-\dfrac{4}{25}-\dfrac{4}{125}-\dfrac{4}{625}}\)
\(=\dfrac{\dfrac{1}{9}-\dfrac{1}{7}-\dfrac{1}{11}}{4\cdot\left(\dfrac{1}{9}-\dfrac{1}{7}-\dfrac{1}{11}\right)}+\dfrac{3\cdot\left(\dfrac{1}{5}-\dfrac{1}{25}-\dfrac{1}{125}-\dfrac{1}{625}\right)}{4\cdot\left(\dfrac{1}{5}-\dfrac{1}{25}-\dfrac{1}{125}-\dfrac{1}{625}\right)}\)
\(=\dfrac{1}{4}+\dfrac{3}{4}=1\)
\(c,\left[\left(\dfrac{2}{193}-\dfrac{3}{386}\right)\cdot\dfrac{193}{17}+\dfrac{33}{34}\right]:\left[\left(\dfrac{7}{2001}+\dfrac{11}{4002}\right)\cdot\dfrac{2001}{25}+\dfrac{9}{2}\right]\)
\(=\left[\dfrac{1}{386}\cdot\dfrac{193}{17}+\dfrac{33}{34}\right]:\left[\dfrac{25}{4002}\cdot\dfrac{2001}{25}+\dfrac{9}{2}\right]\)
\(=\left[\dfrac{1}{2}\cdot\dfrac{1}{17}+\dfrac{33}{34}\right]:\left[\dfrac{1}{4002}\cdot\dfrac{2001}{1}+\dfrac{9}{2}\right]\)
\(=\left[\dfrac{1}{34}+\dfrac{33}{34}\right]:\left[\dfrac{2001}{4002}+\dfrac{9}{2}\right]\)
`= 1 : 5`
`=1/5`