Simple calculation error

Question

I'm missing something stupidly simple here.
A simple script to determine a reimbursement rate for kilometers traveled multiplied by the allowable tax amount (based one engine size).

A log of each step shows the correct values being found, but the final step in the text input with the name=reimbursement attribute is returning "$0".

What am I missing?

function calcRate() {
var engineRate = Number(jQuery( "input[name='enginesize']:checked" ).val());
var distanceTravelled = 0.0;
var distances = new Array();
        distances[0] = Number(jQuery("#field_Distance1").val());
        distances[1] = Number(jQuery("#field_Distance2").val());
        distances[2] = Number(jQuery("#field_Distance3").val());
        distances[3] = Number(jQuery("#field_Distance4").val());
        distances[4] = Number(jQuery("#field_Distance5").val());
    for(var i=0; i<distances.length; i++) {
            if(!isNaN(distances[i])) {
                distanceTravelled = distanceTravelled + distances[i];
            }
        }
    jQuery("input[name=reimbursement]").val("$" + distanceTravelled * engineRate);
    }
jQuery("input[type=radio],input[type=text]").on("change",calcRate);

Answer 1

I changed the sum line to

distanceTravelled += distances[i];

I also swapped the dynamic values with temporary ones, it displayed $150, which is the expected result (and nothing to do with brackets as mentioned by @cbp).

function calcRate() {
    var engineRate = 10;
    var distanceTravelled = 0.0;
    var distances = new Array();
    distances[0] = 1;
    distances[1] = 2;
    distances[2] = 3;
    distances[3] = 4;
    distances[4] = 5;
    for (var i = 0; i < distances.length; i++) {
        if (!isNaN(distances[i])) {
            distanceTravelled += distances[i];
        }
    }
    alert("$" + distanceTravelled * engineRate);
}
calcRate();

http://jsfiddle.net/tcEpF/2/

I then swapped in the jQuery selector for the output text box, it displays $150:

<input name="reimbursement" />

http://jsfiddle.net/tcEpF/3/

Assuming the engine rate are radio buttons, I proceeded to add them in:

<input type="radio" name="enginesize" value="10" />10<br>
<input type="radio" name="enginesize" value="100" />100<br>
<input type="radio" name="enginesize" value="1000" />1000<br>

Clicking on any of them displays the expected results: $150, $1500, $15000

http://jsfiddle.net/tcEpF/4/

I can only conclude that the selector for field_Distance is wrong:

jQuery("#field_Distance1")

You might want to use this instead to get the name of the field, as # means you are getting the ID attribute instead, which is probably missing.

jQuery("input[name=field_Distance1]")

Why is it displaying $0 then? As the selector is wrong, the array now contains NaN values. distanceTravelled remains as 0.0 after the for-loop as !isNaN(distances[i]) returns false, skipping over the sum. In the end, anything multiplied by 0 returns 0.

Answer 2

When in doubt, add brackets:

jQuery("input[name=reimbursement]").val("$" + (distanceTravelled * engineRate));