My workbook has two worksheets:
ALL BILLS
BY TYPE OF BILL

On the TYPE OF BILL worksheet, the values of cells
E8 = 320
E22 = 0
E36 = 0
E50 = 30

On the ALL BILLS tab, I've typed this formula:
=SUM('BY TYPE OF BILL'!E8+E22+E36+E50)

however, the result is 320 not 350.

What's wrong?