Question

5. Tìm phân số a/b biết: A) 4/9 x a/b - 1/9 = 5/27. B) 9/13 x a/b + 1/7 = 40/91.

Answer 1

a: =>4/9*a/b=5/27+3/27=8/27

=>a/bb=8/27:4/9=8/27*9/4=72/108=2/3

b: =>9/13*a/b=40/91+1/7=53/91

=>a/b=53/63

Answer 2

`a)4/9xxa/b-1/9=5/27`

`=>4/9xxa/b=5/27+1/9`

`=>4/9xxa/b=5/27+3/27`

`=>4/9xxa/b=8/27`

`=>a/b=8/27:4/9`

`=>a/b=8/27xx9/4`

`=>a/b=2/3`

Vậy `a=2` và `b=3`

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`b)9/13xxa/b+1/7=40/91`

`=>9/13xxa/b=40/91-1/7`

`=>9/13xxa/b=40/91-13/91`

`=>9/13xxa/b=27/91`

`=>a/b=27/91:9/13`

`=>a/b=27/91xx13/9`

`=>a/b=39/91`

Vậy `a=39` và `b=91`