The price of petrol rises from Rs. 80 to Rs. 100. What is the percentage increase in price?

To find the percentage increase, use the following formula:
$$\text{Percentage Increase}=\left(\frac{\text{Increase in Price}}{\text{Original Price}}\right)\times 100\%$$

Given:

* Original Price = Rs. 80
* New Price = Rs. 100
* Increase in Price = $100-80=20$

Substituting values into the formula:

$$\text{Percentage Increase}=\left(\frac{20}{80}\right)\times 100\%=\frac{1}{4}\times 100\%=25\%$$