Question

define index number​

Answer 1

$\huge\underline\mathfrak{Index\:Number}$

Index numbers are a simple way of making it easier to compare numbers over a period of time. Index numbers measure relative changes in the price of a sum of representative data.

Answer 2

Answer:

An index number is the measure of change in a variable (or group of variables) over time. ... Index numbers are one of the most used statistical tools in economics. Index numbers are not directly measurable, but represent general, relative changes. They are typically expressed as percents

Explanation:

Suppose the price of a commodity changes from 100 to 120 and then from 120 to 180. Here just by looking at this information, we can tell that the price has hiked by 20% and 80% respectively with respect to the initial price. It is situations like these or even more complex ones where the index numbers come in handy. An Index number helps in the calculation of percentage change in a phenomenon with respect to a base parameter.