`a)` `2/3` `+` `3/4` `+` `5/6`
`=` `8/12` `+` `9/12` `+` `10/12`
`=` `(8+9+10)/12`
`=` `27/12` `=` `9/4`
`b)` `1/2` `+` `4/5` `-` `12/25`
`=` `25/50` `+` `40/50` `-` `24/50`
`=` `(25+40-24)/50`
`=` `41/50`
`c)` `5/6` `×` `(4/15+2/3)`
`=` `5/6` `×` `(4/15+10/15)`
`=` `5/6` `×` `14/15`
`=` `(5×14)/(6×15)`
`=` `70/90` `=` `7/9`
`d)` `13/9` `÷` `5/6` `÷` `7/15`
`=` `13/9` `×` `6/5` `×` `15/7`
`=` `(13×6×15)/(9×5×7)`
`=` `1170/315` `=` `26/7`
