Chain Rule: Unitary Methods

1. Direct Proportion
Two quantities are said to be directly proportional, if on the increase or decrease of one, the other increases or decreases the same extent.

Example (a) Sales of the goods is directly proportional to the number of goods sold. (More goods sold, More sale).
(b) Amount of work done i.e., output is directly proportional to the number of work force who were placed to do the work. (More work force, More Work output).

2. Indirect Proportion (inverse proportion)
Two quantities are said to be indirectly proportional (inversely proportional) if on the increase of one, the other decreases to the same extent and vice-versa.

Example (a) Number of days needed to complete a work is indirectly proportional (inversely proportional) to the number of work force employed to do the work (More work force, Lesser Days needed).
(b) The time taken to travel a distance is indirectly proportional (inversely proportional) to the speed of travel (More Speed, Less Time).