Thực hiện từng bước các phép tính sau: a, 3/5 + -9/10 - 7/6 b, 21/36 + 18/7 + -2/3 c, 5/14 + 3/7 : 1/21

Đáp án:

 `a)`

`3/5+\frac{-9}{10}-7/6`

`=\frac{18}{30}+\frac{-27}{30}-\frac{35}{30}`

`=\frac{18+(-27)-35}{30}`

`=\frac{(-9)-35}{30}`

`=\frac{-44}{30}`

`=-22/15`

`b)`

`21/36+18/7+\frac{-2}{3}`

`=7/12+\frac{18}{7}-2/3`

`=49/84+216/84-\frac{56}{84}`

`=\frac{49+216-56}{84}`

`=209/84`

`c)`

`5/14+3/7: 1/21`

`=5/14+ 3/7 . 21`

`=5/14+63/7`

`=5/14+9`

`=5/14+126/14`

`=131/14`