jquery check-uncheck checkbox [duplicate]

This question already has an answer here:

• Setting “checked” for a checkbox with jQuery? 36 answers

When I click on Problem, both check boxes must select/deselect. I want to select and deselect check boxes for multiple time. It works only for selecting and then deselecting (2 times) and then is not working any more.

My code:

 $(document).ready(function() {
        $('#CHECK-ALL').click(function() {
            if ($(this).is(':checked')) {
                $('#P').attr('checked',true);                
            } else {
                $('#P').attr('checked',false);                
            }
        });
    });