Câu 1:
`(12,48 : 0,5 × 6,25 × 4 × 2)/(2 × 3,12 × 1,25 : 0,25 × 10)`
`= (3,12 × 4 × 2 × 1,25 × 5 × 4 × 2)/(2 × 3,12 × 1,25 × 4 × 2 × 5)`
`= 4`
Câu 2:
`12/7 : x + 2/3 = 7/5`
`12/7 : x = 7/5 - 2/3`
`12/7 : x = 21/15 - 10/15`
`12/7 : x = 11/15`
`x = 12/7 : 11/15`
`x = 12/7 . 15/11`
`x = 180/77`