title: Count the number of checkboxlist and if checked items more than 1, check another checkbox?
body: <p>I have a checkboxlist control on my webform page in asp.net like following code:</p>
  
  <pre><code>&lt;div&gt;
  &lt;asp:CheckBoxList ID="CheckBoxList1" runat="server" CssClass="cbxlMulti"&gt;
      &lt;asp:ListItem Value="AAAA"&gt;AAAA&lt;/asp:ListItem&gt;
      &lt;asp:ListItem Value="BBBB"&gt;BBBB&lt;/asp:ListItem&gt;
      &lt;asp:ListItem Value="CCCC"&gt;CCCC&lt;/asp:ListItem&gt;
  &lt;/asp:CheckBoxList&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>this code is parsed into HTML by asp.net:</p>
  
  <pre><code>&lt;div&gt;
  &lt;table id="ContentPlaceHolder1_CheckBoxList1" class="cbxlMulti"&gt;
    &lt;tbody&gt;
      &lt;tr&gt;
        &lt;td&gt;
          &lt;input id="ContentPlaceHolder1_CheckBoxList1_0" type="checkbox" name="ct100$ContentPlaceHolder1$CheckBoxList1$0" value="AAAA"&gt;
          &lt;label for="ContentPlaceHolder1_CheckBoxList1_0"&gt;AAAA&lt;/label&gt;
        &lt;/td&gt;
      &lt;/tr&gt;
      &lt;tr&gt;
        &lt;td&gt;
          &lt;input id="ContentPlaceHolder1_CheckBoxList1_1" type="checkbox" name="ct100$ContentPlaceHolder1$CheckBoxList1$1" value="BBBB"&gt;
          &lt;label for="ContentPlaceHolder1_CheckBoxList1_1"&gt;BBBB&lt;/label&gt;
        &lt;/td&gt;
      &lt;/tr&gt;
      &lt;tr&gt;
        &lt;td&gt;
          &lt;input id="ContentPlaceHolder1_CheckBoxList1_2" type="checkbox" name="ct100$ContentPlaceHolder1$CheckBoxList1$2" value="BBBB"&gt;
          &lt;label for="ContentPlaceHolder1_CheckBoxList1_2"&gt;BBBB&lt;/label&gt;
        &lt;/td&gt;
      &lt;/tr&gt;
  </code></pre>
  
  <p>and another checkbox:</p>
  
  <pre><code>&lt;div&gt;
  &lt;asp:CheckBox ID="CheckBox1" runat="server" CssClass="cbxSingle" Text="XXXX" /&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>I want to whether the number of selected items in CheckBoxlist1 is more than 1, if yes, the CheckBox1 will be auto checked. I would like to achieve this using jQuery.</p>