Using jQuery to change div width from 50% to 70% on hover

Question

I have two divs that have 50% width each. I want to make it so that the the hovered div expands to 70% and the other reduces to 30%. And when the mouse moves out, they both

Answer 1

To take @James' answer (+1) and add animation, just use .animate():

$(function(){
    $("#div1").hover(
        function(){
           $(this).animate({width: '70%'});
        },
        function(){
            $(this).animate({width: '50%'});
        }
    );                            
});

Demo: http://jsfiddle.net/mattball/sAW2c/