php display and total pricing on same page - php

Question

I have been searching for a way to add up the total sum of radio buttons and echo it that total on the same page in php. Is there a way to do this? I have included an image of what I am looking at.
Here is code that I have come up with so far:
PHP
<?php
$prod1 = "10";
$prod2 = "20";
$prod3 = "30";
?>
<form action="">
<input type="radio" name="prod1" value="<?=$prod1?>">$10 product 1<br>
<input type="radio" name="prod2" value="<?=$prod2?>">$20 product 2<br>
<input type="radio" name="prod3" value="<?=$prod3?>">$30 product 3
</form>
<!-- This is where the total shows live upon radio check -->
<?php
echo ="$total"
?>
I am new so it will not post an image, here is a link to my image:

Answer 1

Working example
You need an element where the total is going to be, and a way of identifying those inputs. I've used input which isn't very specific; You may want to change this if you have more going on in that form.
I bound change to the form (which I gave the id products) because the change events made on the inputs will bubble up to the form, and we need to search the whole form for all the inputs so it made sense not to have to traverse, which we'd need to do if the function was bound to the input fields.
Then simply, on change of something in the form, add up the values of the checked elements. parseFloat() is used because the values are strings and you'd end up with "102030" where you really wanted "60".
HTML
<form action="" id="products">
<label><input type="radio" name="prod1" value="10" />$10 product 1</label>
<br />
<label><input type="radio" name="prod2" value="20" />$20 product 2</label>
<br />
<label><input type="radio" name="prod3" value="30" />$30 product 3</label>
</form>
<p>Total $<span id="total">0</span></p>
jQuery
$(function(){
$('#products').on('change', function(){
var total = 0;
$(this).find('input:checked').each(function(){
total += parseFloat($(this).val());
});
$('#total').text(total);
});
});
By the way, if the user is supposed to be able to uncheck these options, you need to use <input type="checkbox" ...