Theory:

Times changes everything. Change is unchangeable, right?
 
Similarly, if one quantity is increasing or decreasing due to time or other factors, we measure it in the percentage of the same to understand the change in a better way.
 
Increase.jpg
Example:
1. The price of the vegetable is increasing due to inflation.
 
2. The water level in a state is decreasing due to a huge consumption and lack of rainfall.
 
3. The temperature will increase in the coming summer due to climate change.

4. The population is increasing over the period.

5. Certain price of the products is decreased because of the festival season offer.
So like the above, all conditions, measuring the changes in one quantity in terms of percentage is helping to understand the particular data or situations better.
 
Now we see how to calculate those changes in quantities in percentage.
 
We can use the below formula to obtain the increase or decrease percentage.
\(\text{Increase / Decrease percentage}\) \(=\) \(\frac{\text{Change in quantity}}{\text{Original quantity}}\)\(\times100\)