"A man owns a digital camera which cost him $400 but is considering buying a new model costing $1000. He could obtain $100 if he sold his digital camera. What is the opportunity cost of him owning his current phone? "

phone = not camera ---(1)
camera = not phone ---(2)

hence,
phone + not phone = camera +not camera
phone (1+not) = camera (1+not)
therefore,
phone = camera ?!?

(o.O)"  ¶ 4:56 PM