The ratio of two quantities a and b in the same units, is the fraction a/b and we write it as a:b .
Ratio 4:8 can be represented as .
The equality of two ratios is called proportion.
If a : b = c : d , we write it as a : b :: c : d , and we say that a, b, c and d are in proportion.
Thus a : b :: c : d => (b * c) = (a * d)
A] Fourth Proportional – If a : b = c : d , then d is called the fourth proportional to a, b, c.
B] Third Proportional - If a : b = b : c , then c is called the third proportional to a and b.
C] Mean Proportional – Mean proportional between a and b is .
The Compound Ratio of the ratios (a : b), (c : d), (e : f) is (ace : bdf)
B] Sub-Duplicate Ratio of (a : b) is
C] Triplicate Ratio of (a : b) is (a3 : b3)
D] Subtriplicate Ratio of (a : b) = (a1/3 : b1/3)
E] Componendo and Dividendo If then