//产生随机数
function rd(){
num = arr[Math.floor(Math.random()*arr.length)]; //获得的随机数
var hundred,figures,theunit;
hundred = Math.floor(num/100);
figures = Math.floor(num%100/10);
theunit = Math.floor(num%10);
//背景变化
$("#num_1").css("background","url(images/"+hundred+".png) no-repeat");
$("#num_2").css("background","url(images/"+figures+".png) no-repeat");
$("#num_3").css("background","url(images/"+theunit+".png) no-repeat");
}