* Sửa đề : `13/28 . x = 1/7 . ( 555/222 + 4444/12221 + 33333/244442 + 11/330 + 13/60 )` ( Đề gặp rồi nên biết )
* Bài làm :
`13/28 . x = 1/7 . ( 555/222 + 4444/12221 + 33333/244442 + 11/330 + 13/60 )`
`⇔ 13/28 . x = 1/7 . ( 5/2 + 4/11 + 3/22 + 1/30 + 13/60 )`
`⇔ 13/28 . x = 1/7 . [ ( 5/2 + 1/30 + 13/60 ) + ( 4/11 + 3/22 ) ]`
`⇔ 13/28 . x = 1/7 . [ ( 150/60 + 2/60 + 13/60 ) + ( 8/22 + 3/22 ) ]`
`⇔ 13/28 . x = 1/7 . [ 11/4 + 1/2 ]`
`⇔ 13/28 . x = 1/7 . [ 11/4 + 2/4 ]`
`⇔ 13/28 . x = 1/7 . 13/4`
`⇔ 13/28 . x = 13/28`
`⇔ x = 13/28 : 13/28`
`⇔ x = 1`
Vậy , `x = 1 .`
