高分求高人,已经实现了秒递减，怎设置分钟递减？
两个button   ,一个显示秒递减，一个显示分钟递减，下面的程序已经实现了秒的递减，怎么设置分钟也会递减啊，求高人指点啊！

<input   type= "button "   id= "agree "   value= "等待时间为 "   onclick= " ' ">
<input   type= "button "   id= "yes "   value= "等待时间为 "   onclick= " ' ">
</BODY>
</HTML>
<script   type= "text/javascript ">
    var   settime=300;
    var   i;
    var   showthis;
    document.all.agree.disabled=true;
    for(i=1;i <=settime;i++)       {
          setTimeout( "update( "+i+ ") ",i*1000);
    }
    function   update(num)   {
          if(num==settime)   {
    document.all.agree.value= "0 ";
    document.all.agree.disabled=false;
      }
      else   {
      showthis=settime-num;
      document.all.agree.value= "等待时间为   ( "+showthis+ ")秒 ";
      }
    }
</script>


------解决方案--------------------
document.all.yes.value= "等待时间为 ( "+parseInt(showthis/60+1)+ ") 分 ";
------解决方案--------------------
<input type= "button " id= "agree " value= "等待时间为 " onclick= " ">
<input type= "button " id= "yes " value= "等待时间为 " onclick= " ">
</BODY>
</HTML>
<script type= "text/javascript ">
var settime=300;
var i;
var showthis;
document.all.agree.disabled=true;
for(i=1;i <=settime;i++) {
setTimeout( "update( "+i+ ") ",i*1000);
}
function update(num) {
if(num==settime) {
document.all.agree.value= "0 ";
document.all.agree.disabled=false;
}
else {
showthis=settime-num;
document.all.yes.value= "等待时间为 ( "+ Math.round(parseFloat(showthis/60)*100)/100+ ")分钟 ";
document.all.agree.value= "等待时间为 ( "+showthis+ ")秒 ";
}
}
</script>