Is it possible to have part of a link (or the whole link) to change depending on the selected item in a drop-down menu within a form?

Here's what my link will look like...

HTML Code:
<a href="http://www.calculator.com/calculate.php?weight=2.5kg&country=England">Calculator</a>
The 'England' part of the string would be only chunk which would need to be changed when a different item is selected in the drop-down. I'm assuming something like this would do the trick...

HTML Code:
<select onchange="change_link(link)">
<option value="Australia">Australia</option>
<option value="England">England</option>
</select>

<a href="http://www.calculator.com/calculate.php?weight=2.5kg&country=England" id="link">Calculator</a>
I'm just not sure of what you'd put in the change_link function as I'm a bit of a 'n00b' when it comes to javascript. In the end though, I want the value of the currently selected item in the drop-down, to replace the value of 'country' in the link/url.

Thanks!