产生两个随机数，并且两个随机数之和为固定值
function num(lbound, ubound) {
return (Math.floor(Math.random() * (ubound - lbound)) + lbound);
}
var x=num(0,24);
var z = 24;
var y = z - x;
document.write(x);
document.write("<br>");
document.write(y);
原文：http://www.cnblogs.com/jasontoyell/p/4693378.html