Bài tính:
`d, 2/21 - (-1)/28`
`= 2/21 + 1/28`
`= 8/84 + 3/84`
`= 11/84`
`e, 3/4 - [ (-5/3) - (1/12 + 2/9) ]`
`= 3/4 - [ (-5/3) - (3/36 + 8/36) ]`
`= 3/4 - [ (-5/3) - 11/36 ]`
`= 3/4 - [ (-60/36) - 11/36 ]`
`= 3/4 - (-71)/36`
`= 27/36 + 71/36`
`= 98/36 = 49/18`
Bài tìm x:
`(-2)/15 - x = (-3)/10`
`x = (-2)/15 - (-3)/10`
`x = (-2)/15 + 3/10`
`x = (-4)/30 + 9/30`
`x = 5/30 = 1/6`
Vậy `x = 1/6`
