Giải thích các bước giải:
a) $\frac{15-x}{9}=\frac{1}{3}$
`=>` (15-x) . 3 = 9
`=>` 15-x =3
`=>` x=15-3=12
b)35<x.6+5<125
`=>` 5.6+5<x.6+5<20.6+5
`=>` 5<x<20
`=>` x={6;7;8;..;19}
c)20:x+10:x=50
`=>` (20+10):x=50
`=>` 30:x=50
`=>` $\frac{3}{5}$
d)x:5+x:7=12
`=>` x:(5+7)=12
`=>` x:12=12
`=>` x=144
e)x:9.2+x:5.15+x=1
`=>` x.2/9+x.3+x=1
`=>` x(1/9+3+1)=1
`=>` x.$\frac{29}{9}$=1
`=>` x =$\frac{9}{29}$
g)555:37.x=5
`=>` 15.x=5
`=>` x=$\frac{1}{3}$
h)185-x.8:2=21
`=>` x.4=164
`=>` x=41
