**Important Concepts and Formulas**

2. While calculating the ratio of two
given quantities, both the quantities must be in the same unit.

3. The ratio a : b is not same as the
ratio b : a.

4. The first term of a ratio is called
the antecedent and the second term is called the consequent.

5. Normally a ratio is expressed in its
simplest form.

6. The ratios a : b and c : d are
equivalent ratios if a/b and c/d are equivalent fractions.

7. We can compare two ratios by converting
the ratios in their fractional forms.

8. Two equal ratios are said to be in
proportion.

10. First and fourth terms (end terms) of
a proportion are called extremes and the middle terms (i.e., the second and
third terms) are called means.

11. If four terms are in proportion, then
product of extremes = product of means.

12. The rule ad = bc is used to check
whether a, b, c, d are in proportion or not.

13. A method in which we first find the
value of one unit and then the value of the required number of units is called
unitary method.