将 switch 类移动到外部 div，像这样

Move the switch class to an outter div, like so

<div class="switch">
<div class="avg_words float_left">
  A+ (hover to see score)  
</div>
<div class="avg_num">
  AVG = 98.35%
</div>
</div>

$('.switch').hover(function() {
        $(this).find('.avg_words').hide();
        $(this).find('.avg_num').show();
    }, function() {
        $(this).find('.avg_num').hide();
        $(this).find('.avg_words').show();
});

更新的小提琴:http://jsfiddle.net/uXeg2/2/