Ive a list with 10 checkboxes and I as wondering if there are any way of enable a submit button only when 3 of them are checked.

I've this code but it enables de button if any checkbox is checked.

HTML Code:
<script type="text/javascript">
function enviar(){
    document.form.aceptar.disabled = true;
    for (i=0;i<document.form.elements.length;i++){
        if(document.form.elements[i].type == "checkbox"){
            if(document.equipo.elements[i].checked == 1 ){
                document.form.aceptar.disabled = false;
Any clue would be great!