解:(1)1.5+1.8x=10.2,
1.5+1.8x-1.5=10.2-1.5,
1.8x=8.7,
1.8x÷1.8=8.7÷1.8,
x=
;
(2)x+1.6x=0.39,
(1+1.6)x=0.39,
2.6x=0.39,
2.6x÷2.6=0.39÷2.6,
x=0.15;
(3)3.9(x-1.6)=15.6,
3.9x-3.9×1.6=15.6,
3.9x-6.24=15.6,
3.9x-6.24+6.24=15.6+6.24,
3.9x=21.84,
3.9x÷3.9=21.84÷3.9,
x=5.6;
(4)
(x+
)=
,
(x+
)÷
=
÷
,
x+
=
,
x+
-
=
-
,
x=
;
(5)
x+
x=
,
(
+
)x=
,
x=
,
x÷
=
÷
,
x=
;
(6)1.5x+x-
x=4,
(1.5+1-
)x=4,
2x=4,
x=2;
(7)(1-
)x=350,
x=350,
x÷
=350÷
,
x=450;
(8)x+25%x=40,
(1+25%)x=40,
1.25x=40,
1.25x÷1.25=40÷1.25,
x=32.
分析:我们运用等式的基本性质进行解答,即,等式的两边同时加上或减去同一个数,等式仍然成立;等式的两边同时乘以或除以同一个不为零的数,等式仍然成立.
点评:本题运用等式的基本性质进行解答即可.注意等号要对齐.