解:(1)
![](http://thumb.1010pic.com/pic5/latex/1114.png)
:x=
![](http://thumb.1010pic.com/pic5/latex/365.png)
:
![](http://thumb.1010pic.com/pic5/latex/155.png)
,
![](http://thumb.1010pic.com/pic5/latex/365.png)
x=
![](http://thumb.1010pic.com/pic5/latex/520261.png)
,
![](http://thumb.1010pic.com/pic5/latex/365.png)
x×
![](http://thumb.1010pic.com/pic5/latex/304.png)
=
![](http://thumb.1010pic.com/pic5/latex/520261.png)
×
![](http://thumb.1010pic.com/pic5/latex/304.png)
,
x=
![](http://thumb.1010pic.com/pic5/latex/2367.png)
;
(2)3x+
![](http://thumb.1010pic.com/pic5/latex/13.png)
=
![](http://thumb.1010pic.com/pic5/latex/1231.png)
,
3x+
![](http://thumb.1010pic.com/pic5/latex/13.png)
![](http://thumb.1010pic.com/pic5/latex/479.png)
=
![](http://thumb.1010pic.com/pic5/latex/520262.png)
,
3x=
![](http://thumb.1010pic.com/pic5/latex/7580.png)
,
3x÷3=
![](http://thumb.1010pic.com/pic5/latex/7580.png)
÷3,
x=
![](http://thumb.1010pic.com/pic5/latex/23375.png)
;
(3)x-25%x=27,
0.75x=27,
0.75x÷0.75=27÷0.75,
x=36.
分析:(1)先利用比例的基本性质,把这个比例变形为一个一元一次方程:
![](http://thumb.1010pic.com/pic5/latex/365.png)
x=
![](http://thumb.1010pic.com/pic5/latex/520261.png)
,再利用等式的性质,两边同时乘以
![](http://thumb.1010pic.com/pic5/latex/304.png)
即可求得x的值;
(2)利用等式的性质,先把方程的两边同时减去
![](http://thumb.1010pic.com/pic5/latex/13.png)
,再除以3即可;
(3)先把左边的式子整理,得到0.75x=27,再利用等式的性质,两边同时除以0.75即可.
点评:此题考查了利用等式的性质解一元一次方程以及利用比例的基本性质解比例的灵活应用.