Đáp án `+` Giải thích các bước giải:

 a) `1/6 - (-5)/6`

`= 1/6 + 5/6`

`= 6/6 = 1.`

b) `6/13 - (-14)/39`

`= 6/13 + 14/39`

`= 18/39 + 14/39`

`= 32/39.`

c) `4/5 - 4/(-18)`

`= 4/5 + 4/18`

`= 72/90 + 20/90`

`= 92/90 = 46/45.`

d) `7/21 - 9/(-36)`

`= 1/3 + 9/36`

`= 1/3 + 1/4`

`= 4/12 + 3/12`

`= 7/12.`

e) `(-12)/18 - (-21)/35`

`= (-2)/3 + 21/35`

`= (-2)/3 + 3/5`

`= (-10)/15 + 9/15`

`= (-1)/15.`

f) `(-3)/21 - 6/42`

`= (-1)/7 - 1/7`

`= (-2)/7.`

g) `(-18)/24 - 15/21`

`= (-3)/4 - 5/7`

`= (-21)/28 - 20/28`

`= (-41)/28.`

h) `3/5 - (-7)/4`

`= 3/5 + 7/4`

`= 12/20 + 35/20`

`= 47/20.`

j) `(-(-1))/21 - 1/28`

`= 1/21 - 1/28`

`= 4/84 - 3/84`

`= 1/84.`

k) `8/40 - (-36)/45`

`= 1/5 + 4/5`

`= 5/5 = 1.`

l) `13/30 - (-1)/5`

`= 13/30 + 1/5`

`= 13/30 + 6/30`

`= 19/30.`

m) `5 - (-3)/4`

`= 5 + 3/4`

`= 20/4 + 3/4`

= 23/4.