(1)
1
3 :
1
20 =
7
9 :x
1
3 x=
1
20 ×
7
9 ,
1
3 x×3=
7
180 ×3 ,
x=
7
60 ;
(2)8.4+40%x=12,
8.4+0.4x-8.4=12-8.4,
0.4x÷0.4=3.6÷0.4,
x=9;
(3)8x+6x=7×12
14x=84,
14x÷14=84÷14,
x=6;
(4)
3
4 x-1=
1
2 ,
3
4 x -1+1=
1
2 +1 ,
3
4 x×
4
3 =
3
2 ×
4
3 ,
x=2.
(1)
1
3 :
1
20 =
7
9 :x
1
3 x=
1
20 ×
7
9 ,
1
3 x×3=
7
180 ×3 ,
x=
7
60 ;
(2)8.4+40%x=12,
8.4+0.4x-8.4=12-8.4,
0.4x÷0.4=3.6÷0.4,
x=9;
(3)8x+6x=7×12
14x=84,
14x÷14=84÷14,
x=6;
(4)
3
4 x-1=
1
2 ,
3
4 x -1+1=
1
2 +1 ,
3
4 x×
4
3 =
3
2 ×
4
3 ,
x=2.