In the following questions, which of them vary directly and which vary inversely with each other and which are neither of the two?
(i) Number of students in a hostel and consumption of food
(ii) Area of the walls of a room and the cost of white washing the walls.
(iii) The number of people working and the quantity of work.
(iv) Simple interest on a given sum and the rate of interest
(v) Compound interest on a given sum and the sum invested.