1.Rút gọn phân số rồi tính a 35/60 + 4/16 b 63/90 + 7/21

$a)$

`35/60 + 4/16`

`= 7/12 + 1/4`

`= 7/12 + 3/12`

`= \frac{7+3}{12}`

`= 10/12`

`= 5/6`

`b)`

`63/90 + 7/21`

`= 7/10 + 1/3`

`= 21/30 + 10/30`

`= \frac{21+10}{30}`

`= 31/30`