解:(1)

-5x=0.125,
0.125+5x=

,
0.125+5x-0.125=

-0.125,
5x=0.25,
5x÷5=0.25÷5,
x=0.05;
(2)x:0.2=

,
x÷0.2=

,
x÷0.2×0.2=

×0.2,
x=0.125;
(3)12X+7×0.3=20.1,
12X+2.1=20.1,
12X+2.1-2.1=20.1-2.1,
12X=18,
12X÷12=18÷12,
X=1.5;
(4)

X+

X=1.2,

X=1.2,

X÷

=1.2÷

,
X=1.44.
分析:(1)等式的兩邊同時(shí)加上5x,原始改寫(xiě)為0.125+5x=

,等式的兩邊同時(shí)減去0.125,等式的兩邊同時(shí)除5即可;
(2)根據(jù)比與除法的關(guān)系,原始改寫(xiě)為x÷0.2=

,然后等式的兩邊同時(shí)乘0.2即可;
(3)先計(jì)算7×0.3=2.1,等式的兩邊同時(shí)減去2.1,然后等式的兩邊再同時(shí)除12即可;
(4)先計(jì)算

X+

X=

X,然后等式的兩邊再同時(shí)除以

即可.
點(diǎn)評(píng):本題主要考查解比例和解方程,根據(jù)比例的基本性質(zhì)和等式的性質(zhì)進(jìn)行解答即可.