I have a script which returns a decimal value to represent time. I need to convert the decimal time value to hh:mm (i.e: 90 minutes decimal value 1.5 should be represented as 1:30. Having trouble figuring this out. Attached is my current script.

Code:
<script>
function Convert() {
    var minutes = document.getElementById("sum").value;
    var hours = minutes / 60;
    document.getElementById('total').value = hours;
    document.getElementById('sum').value = minutes;
var convert = function (sum) {
    return Math.floor(sum/60) + ":" + (sum-Math.floor(sum/60)*60);
}

 
</script>