解:(1)X:2=5:0.4,
0.4x=2×5,
0.4x=10,
0.4x÷0.4=10÷0.4,
x=25;
(2)15.3-3X=0.3,
15.3-3X+3x=0.3+3x,
15.3-0.3=0.3+3x-0.3,
15÷3=3x÷3,
x=5;
(3)
![](http://thumb.1010pic.com/pic5/latex/155.png)
x-
![](http://thumb.1010pic.com/pic5/latex/365.png)
x=0.7+2.3,
![](http://thumb.1010pic.com/pic5/latex/189208.png)
=3,
![](http://thumb.1010pic.com/pic5/latex/6.png)
x
![](http://thumb.1010pic.com/pic5/latex/219549.png)
=3
![](http://thumb.1010pic.com/pic5/latex/219549.png)
,
x=36.
分析:(1)根据比例基本性质:两内项之积等于两外项之积,化简方程,再依据等式的性质,方程两边同时除以0.4求解,
(2)依据等式的性质,方程两边同时加3x,再同时减0.3,最后同时除以3求解,
(3)先化简方程,再依据等式的性质,方程两边同时除以
![](http://thumb.1010pic.com/pic5/latex/6.png)
求解.
点评:等式的性质,以及比例基本性质是解方程的依据,解方程时注意对齐等号.