如何控制概率？思路怎么

怎么控制概率？思路如何?
我想这样的，一个转盘分成4块，可是怎么控制他们的概率不一样呢？要怎么写？

想不下去啊。。。。。求指引~chance为概率

<br />$lottery_arr=array(<br />	"0"=>array("id"=>1,"min"=>0,"max"=>90,"chance"=>10),<br />	"1"=>array("id"=>2,"min"=>90,"max"=>180,"chance"=>20),<br />	"2"=>array("id"=>3,"min"=>180,"max"=<a>本2文来*源gao($daima.com搞@代@#码(网</a><strong>搞gaodaima代码</strong>>270,"chance"=>30),<br />	"3"=>array("id"=>4,"min"=>270,"max"=>360,"chance"=>40),<br />	)<br />

Hi，您需要填写昵称和邮箱！