`a, 4 1/2 . ( 2,5 - 3 3/4 ) + ( - 1 )/2`
`= 9/2 . ( 5/2 - 15/4 ) + ( - 1 )/2`
`= 9/2 . ( - 5 )/4 + ( - 1 )/2`
`= ( - 45 )/8 + ( - 1 )/2`
`= ( - 49 )/8`
`b, - 0,6 . x - 7/3 = 5,4`
`⇔ ( - 3 )/5 . x - 7/3 = 27/5`
`⇔ ( - 3 )/5 . x = 27/5 + 7/3`
`⇔ ( - 3 )/5 . x = 116/15`
`⇔ x = 116/15 : ( - 3 )/5`
`⇔ x = ( - 116 )/9`
Vậy `, x = ( - 116 )/9 .`
`c, 2,8 : ( 1/5 - 3 . x ) = 1 2/5`
`⇔ 14/5 : ( 1/5 - 3 . x ) = 7/5`
`⇔ 1/5 - 3x = 14/5 : 7/5`
`⇔ 1/5 - 3x = 2`
`⇔ 3x = 1/5 - 2`
`⇔ 3x = ( - 9 )/5`
`⇔ x = ( - 9 )/5 : 3`
`⇔ x = ( - 3 )/5`
Vậy `, x = ( - 3 )/5 .`
