function mph_calculator(imiles, iminutes){
   mph = (60 * imiles) / iminutes;
   mph = conv_number(mph,2);
   return mph;
}

function min_calculator(imiles, mph){
   minutes = (60 * imiles) / mph;
   minutes = conv_number(minutes,2);
   return minutes;
}

function conv_number(expr, decplaces){      
     var str = "" + Math.round(eval(expr) * Math.pow(10,decplaces));
     while (str.length <= decplaces) {
           str = "0" + str;
     }
     var decpoint = str.length - decplaces;
     return (str.substring(0,decpoint) + "." + str.substring(decpoint,str.length));}