вот ваш код:
$('.cb1 , .cb2, .cb3').on('change', function(){
Updatesum();
});
function Updatesum() {
var sum1 = 0 ,sum2 = 0 ,sum3 = 0 ;
/* $('.cb:checked').each(function(){
sum += Number($(this).val());
}) */
$('.cb1:checked').each(function(){
// alert('hi');
sum1 += Number($(this).val());
})
$('.cb2:checked').each(function(){
sum2 += Number($(this).val());
})
$('.cb3:checked').each(function(){
sum3 += Number($(this).val());
})
$('#totalsum').val(sum1+sum2+sum3);
$('#total').val(sum1*sum2*sum3);
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<input type="checkbox" class="cb1" value="1" />Game 1 (1)
<input type="checkbox" class="cb1" value="1" />Game 1 (1)
<input type="checkbox" class="cb1" value="1"/> Game 1(1)
<br>
<br>
<input type="checkbox" class="cb2" value="1" />Game 2 (1)
<input type="checkbox" class="cb2" value="1" />Game 2 (1)
<input type="checkbox" class="cb2" value="1"/> Game 2(1)
<br>
<br>
<input type="checkbox" class="cb3" value="1" />Game 3 (1)
<input type="checkbox" class="cb3" value="1" />Game 2 (1)
<input type="checkbox" class="cb3" value="1"/> Game 3(1)
<br>
<input type="text" id="totalsum" value=""/>
<input type="text" id="total" value=""/>
js fiddle: https://jsfiddle.net/6nbrxd2w/