RATIO AND PROPORTION - IMPORTANT FORMULAS
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- Ratio:The ratio of two quantities a and b in the same units, is the fraction
and we write it as a : b.In the ratio a : b, we call a as the first term or antecedent and b, the second term or
consequent.Eg. The ratio 5 : 9 represents 5 with antecedent = 5, consequent = 9. 9
Rule: The multiplication or division of each term of a ratio by the same non-zero number does not affect the ratio.Eg. 4 : 5 = 8 : 10 = 12 : 15. Also, 4 : 6 = 2 : 3.
- Proportion:The equality of two ratios is called proportion.If a : b = c : d, we write a : b :: c : d and we say that a, b, c, d are in proportion.Here a and d are called extremes, while b and c are called mean terms.Product of means = Product of extremes.Thus, a : b :: c : d
(b x c) = (a x d).
- Fourth Proportional:If a : b = c : d, then d is called the fourth proportional to a, b, c.
Third Proportional:a : b = c : d, then c is called the third proportion to a and b.
Mean Proportional:Mean proportional between a and b is ab.
- Comparison of Ratios:
We say that (a : b) > (c : d) a > c . b d
Compounded Ratio:The compounded ratio of the ratios: (a : b), (c : d), (e : f) is (ace : bdf).
- Duplicate Ratios: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).
Sub-triplicate ratio of (a : b) is (a1/3 : b1/3).
If a = c , then a + b = c + d . [componendo and dividendo] b d a - b c - d - Variations:We say that x is directly proportional to y, if x = ky for some constant k and we write, x
y.
We say that x is inversely proportional to y, if xy = k for some constant k and
we write, x 1 . y
This post was written by: Rajendra Prasad
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