Hide Ribbon From members/Visitors group in SharePoint 2010

Open Sharepoint Designer to change the master page as instructed

Find below line:
<div id="s4-ribbonrow" class="s4-pr s4-ribbonrowhidetitle">

Replace it with:
<div id="s4-ribbonrow" class="s4-pr s4-ribbonrowhidetitle" style="display:none">

Now find the end of the “s4-ribbonrow” tag and add following block right after it:

<Sharepoint:SPSecurityTrimmedControl ID="SPSecurityTrimmedControl2" runat="server" PermissionsString="AddAndCustomizePages">  
<script type="text/javascript">
    document.getElementById("s4-ribbonrow").style.display = "block";
</script>
Sharepoint:SPSecurityTrimmedControl>