Let Selling price of One Notepad be 100
Selling Price of 12 Notepads =1200
Profit on Selling 12 Notepads= Selling Price of 4 Notepads =400
Cost on Selling 8 Notepafs=1200-400=800
Percentage Profit on Cost=400/800-50%
Percentage Profit on Sales=400/1200-33.33%