`( y - 2/5) xx 1/2 = 1`
`( y - 2/5) = 1 : 1/2`
`y - 2/5 = 2`
`y = 2 + 2/5`
`y = 10/5 + 2/5`
`y = 12/5`
vậy `x = 12/5`
``
`( y + 4/21) : 3 = 2`
`( y + 4/21) = 2 xx 3`
`y + 4/21 = 6`
`y = 6 - 4/21`
`y = 126/21 - 4/21`
`y = 122/21`
Vậy `y = 122/21`
``
`1 1/2 xx y + y xx 2 3/4 = 17`
`3/2 xx y + y xx 11/4 = 17`
`( 3/2 + 11/4) xx y = 17`
`17/4 xx y = 17`
`y = 17 : 17/4`
`y = 4`
Vậy `y = 4`