jQuery：not（：checked）不起作用？

我有以下HTML：

<form class="pricing-downloads-right pricing-last-form" action="">
    <div class="pricing-levels-top-2">
        <input class="pricing-single-level" type="radio" name="sex" value="male"><strong>Single Level Download $49.95:</strong> Choose a single level (1 to 7) and receive access to all lessons, PDFs and review audio for that level, plus 30 days of online access ($80 value). Email us your level choice after purchase.<br>
        <input class="pricing-3-level-download" type="radio" name="sex" value="male"><strong>3 Level Download $99.95:</strong> Choose any 3 levels (1 to 7) and receive access to all lessons, PDFs and review audio for those levels, plus 60 days of online access ($190 value). Email us your level choices after purchase.<br>
        <input class="pricing-all-access-package" type="radio" name="sex" value="male"><strong>All Access Package $199.9:</strong> Receive access to all lessons, PDFs and review audio for all 7 levels, plus 90 days of online access ($300 value).<br>
    </div>
    <div class="pricing-levels-2">
        <p>Which level would you like? (Click all that apply)</p>
        <input type="checkbox" name="vehicle" value="Bike">Level 1<br>
        <input type="checkbox" name="vehicle" value="Bike">Level 2<br>
        <input type="checkbox" name="vehicle" value="Bike">Level 3<br>
        <input type="checkbox" name="vehicle" value="Bike">Level 4<br>
        <input type="checkbox" name="vehicle" value="Bike">Level 5<br>
        <input type="checkbox" name="vehicle" value="Bike">Level 6<br>
        <input type="checkbox" name="vehicle" value="Bike">Level 7<br>
    </div>
</form>

和jQuery：

jQuery('.pricing-downloads-right input[type=radio]').on('change', function(){
    if(jQuery('.pricing-levels-top-2 input.pricing-single-level:checked').length > 0){                 
          //since you don't want to target by name
          jQuery('.pricing-levels-2').show();
    }
});

jQuery('.pricing-downloads-right input[type=radio]').on('change', function(){
    if(jQuery('.pricing-levels-top-2 input.pricing-single-level:not(:checked)').lenght > 0){ 
           //since you don't want to target by name
           jQuery('.pricing-levels-2').hide();
    }
});

所以我想.pricing-levels-2在input.pricing-single-level选中时显示，而在未选中时隐藏。

现在.pricing-levels-2在input.pricing-single-level选中时显示，但是在未选中时不会隐藏。

我做错了什么？