Hi, why heating and light cost is apportioned on the base of floor area? A department might be small in area but may consume power more than a large department. i can not understood why it is a reasonable base for this?
It is not a rule that heat and light are apportioned on the basis of floor area. In practice you do whatever you think best.
In exam questions you have to make the most sensible use of the information available. In the question you are referring to, there is no other basis that is at all suitable!