Đáp án + Giải thích các bước giải:
a)
`\frac{-1}{9} - \frac{5}{12}`
`= \frac{-4}{36} - \frac{15}{36}`
`= \frac{-19}{36}`
b)
`(\frac{5}{7} - \frac{7}{5}) - [\frac{1}{2} - (\frac{-2}{7} - \frac{1}{10}] `
`= \frac{25}{35} - \frac{49}{35} - (\frac{1}{2} - \frac{-20}{70} - \frac{7}{70})`
`= \frac{-24}{35} - (\frac{1}{2} - \frac{-27}{70})`
`= \frac{-24}{35} - (\frac{35}{70} - \frac{-27}{70})`
`= \frac{-24}{35} - \frac{62}{70}`
`= \frac{-48}{70} - \frac{62}{70}`
`= \frac{-11}{7}`
c)
`\frac{4}{5} + \frac{2}{7} - 0 ,7`
`= \frac{28}{35} + \frac{10}{35} - \frac{7}{10}`
`= \frac{38}{35} - \frac{7}{10}`
` = \frac{76}{70} - \frac{49}{70}`
`= \frac{27}{70}`