1. Rule of three:- The method of finding the 4th proportional when the other three are given is called simple proportion or Rule of Three.
2. Direct Proportion:- Two quantities are said to be directly proportional, if on the increase (or decrease) of the one, the other increases (or decreases) to the same extent. E.g:- (i) More articles, More cost (ii) More men, More work
3. Indirect Proportion:- Two quantities are said to be indirectly proportional, if on the increase of the one, the other decreases to the same extent and vice-versa. E.g:- (i) More men, Less days (ii) More speed, Less time taken.