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). | |
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Variation : (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. |