1. The ratio a : b represents a fraction a/b. a is called antecedent and b is called consequent.

2. The equality of two different ratios is called proportion.

3. If a : b = c : d then a, b, c, d are in proportion. This is represented by a : b :: c : d.

4. In a : b = c : d, then we have a* d = b * c.

5. If a/b = c/d then ( a + b ) / ( a – b )= ( d + c ) / ( d – c ).