<script type="text/javascript">
    
    jQuery(function(){
      jQuery(".div-to-hide-by-default").hide();
      jQuery("#btn-to-make-div-appear").click(function () {
        jQuery(".div-to-hide-by-default").toggle("slow");
        jQuery(".Other-similar-div-already-opened").hide("slow");
         
      });
    });
    
    
</script>