set asp.net dropdown selected value with jquery -

i have code should work fine setting selected value on asp.net dropdownlist reason doesn't want work in case although works in other projects i've been working on. dropdown:

  <asp:dropdownlist id="ddlperc" runat="server">                              <asp:listitem value="">select percentage</asp:listitem>                              <asp:listitem value="0.01">0.01</asp:listitem>                              <asp:listitem value="0.05">0.05</asp:listitem>                          <asp:listitem value="0.1">0.1</asp:listitem>                                <asp:listitem value="0.15">0.15</asp:listitem>                              <asp:listitem value="0.2">0.2</asp:listitem>                                  <asp:listitem value="0.25">0.25</asp:listitem>                                <asp:listitem value="0.3">0.3</asp:listitem>                                 <asp:listitem value="0.4">0.4</asp:listitem>                                                                                              <asp:listitem value="0.48">0.48</asp:listitem>                                                                                                <asp:listitem value="0.5">0.5</asp:listitem>                              <asp:listitem value="0.52">0.52</asp:listitem>                                    <asp:listitem value="0.6">0.6</asp:listitem>                              <asp:listitem value="0.7">0.7</asp:listitem>                              <asp:listitem value="0.75">0.75</asp:listitem>                                                                                                <asp:listitem value="0.8">0.8</asp:listitem>                                                               <asp:listitem value="0.85">0.85</asp:listitem>                                  <asp:listitem value="0.9">0.9</asp:listitem>                                                               <asp:listitem value="0.95">0.95</asp:listitem>                              <asp:listitem value="0.99">0.99</asp:listitem>                              <asp:listitem value="1">1</asp:listitem>                              </asp:dropdownlist> 

and jquery code should work this:

  $(document).on("click", ".open-addbookdialog", function () {                                                      var sign = "1";          $('dropdownagentperc option')         .filter(function () { return $.trim($(this).val()) == sign; })          .attr('selected', true);               $('#addbookdialog').modal('show'); 

when checking source of page can see value has tag selected true in modal popup value still not selected. idea can reason? in advance, laziale

try

.prop('selected', true); 

instead of

.attr('selected', true);