VPT 311: General and Systemic Veterinary Pharmacology (2+1)

RATIO AND PROPORTION 

Ratio

• The relative magnitude of two like quantities is called their ratio. It is also the quotient of two like numbers and can be expressed as a fraction.

Proportion

• It is the expression of equality of two ratios. It may be written as in one of the forms mentioned below.

1. a : b = c : d

2. a : b :: c : d

3. a / b = c / d

• The above expression is to be read as:

‘a is to b as c is to d’

• The terms 'a' and 'd' are called the extremes and the terms 'b' and 'c' are called the means.
• It follows that
  • the product of the means is equal to the product of the extremes and that any missing term can be determined by any of the following formulae:

a = b x c / d;

b = a x d / c:

c = a x d / b and

d = b x c / a

( Note: a and b indicate like-terms and c and d indicate the other set of like-terms)

• Most of the proportions that we come across in pharmacy have direct relationship i.e. as one term increases the other term also increases. But there are also instances of inverse relationship such as change in quantity of solution along with its strength / concentration.
• Most problems in pharmacy can be solved by using proportions.