Đáp án:
Giải thích các bước giải:
`13) x - 120 : 30 = 40`
`x - 4 = 40`
`x = 40 + 4`
`x = 44`
`15) ( x + 5 ) . 3 = 300`
`x + 5 = 300 : 3`
`x + 5 = 100`
`x = 100 - 5`
`x = 95`
`17) x . 14 - x . 2 = 120`
`x . ( 14 - 2 ) = 120`
`x . 12 = 120`
`x = 120 : 12`
`x = 10
`19) 28 . x - x . 17 - x = 250`
`x . ( 28 - 17 - 1 ) = 250`
`x . 10 = 250`
`x = 250 : 10`
`x = 25`
`21) x . 34 - x . 14 = 200`
`x . ( 34 - 14 ) = 200`
`x . 20 = 200`
`x = 200 : 20`
`x = 10`
`14) ( x + 120 ) : 20 = 8`
`x + 120 = 8 . 20`
`x + 120 = 160`
`x = 160 - 120`
`x = 40`
`16) x . 2 + 21 : 3 = 27`
`x . 2 + 7 = 27`
`x . 2 = 27 - 7`
`x . 2 = 20`
`x = 20 : 2`
`x = 10`
`18) x . 13 - x . 10 = 240`
`x . ( 13 - 10 ) = 240`
`x . 3 = 240`
`x = 240 : 3`
`x = 80`
`20) x . 5 - x . 2 = 30`
`x . ( 5 - 2 ) = 30`
`x . 3 = 30`
`x = 30 : 3`
`x = 10`
`22) x . 16 - x . 14 - x = 2`
`x . ( 16 - 14 - 1 ) = 2`
`x . 1 = 2`
`x = 2`
