Ratio and Proportion -> IMPORTANT FACTS AND FORMULAE
|Ratio : The ratio of two quantities a and b in the same units, is the fraction a/b and we write it as a : b.|
|Proportion : The equality of two ratios is called proportion.|
|Mean Proportional : Mean Proportional between a and b is √ab.|
|Fourth Proportional : If a : b = c : d, then d is called the fourth proportional to a,b,c.|
|Third Proportional : If a : b = b : c, then c is called the third proportional to a and b.|
|Duplicate ratio : of (a : b) is (a2 : b2).|
|Sub-duplicate ratio : of (a : b) is (√a : √b).|
|Triplicate ratio : of (a : b) is (a3 : b3).|
(I). We say that x is directly proportional to y, if x = ky for some constant k and we write, x∝y.
(II). We say that x is inversely proportional to y, if xy = k for some constant k and we write, x∝1/y.