Đáp án:
Câu 13:
`A = -7/8 . 5/9 - 4/9 . 7/8 + 5 7/8`
`A = 7/8 . -5/9 - 4/9 . 7/8 + 47/8`
`A = 7/8 . (-5/9 - 4/9) + 47/8`
`A = 7/8 . (-1) + 47/8`
`A = (-7/8) + 47/8`
`A = 40/8`
`A = 5`
Câu 14:
`4/7 . x = 8/9 - 0,125`
`4/7 . x = 8/9 - 1/8`
`4/7 . x = 64/72 - 9/72`
`4/7 . x = 55/72`
`x = 55/72 : 4/7`
`x = 55/72 . 7/4`
`x = 385/288`
Vậy `x = 385/288`