Classic Dice Rule

Hello

I want to know classic dice rule. so i maked a simple example for this.

There is 3 field:

Code:

Roll Under:
<input type="text" id="roll" value="50.00">

Win Chance:
<input type="text" id="chance" value="50.0000">

Multiplier (Payout):
<input type="text" id="multiplier" value="1.9800">

And javascript code:

Code:

$('#range').change(function(e){

let val = parseFloat($(this).val());

$('#roll').val(val.toFixed(2));
$('#chance').val(val.toFixed(4));
$('#multiplier').val('How can calculate');

})

multiplier field have a formula. How can calculate this field ?