What percentage of profit on cost price equals 20% of profit on selling price?

Correct option is C

Given:
 20% of profit on selling price
Formula Used:
Profit = Selling Price - Cost Price
When Profit Percentage is calculated on Selling Price then, Profit Percentage = $$\left(\frac{\text{Profit}}{\text{Selling Price}}\right) \times 100$$
​When Profit Percentage is calculated on Cost Price then, Profit Percentage = $$\left(\frac{\text{Profit}}{\text{Cost Price}}\right) \times 100$$​
Solution:
Let the selling price be 100x
=> Profit = 20% of the selling price
=> Profit = 20% × 100x = 20x
Cost price = selling price – Profit
=> Cost price = 100x – 20x = 80x
Profit% on the cost price = $$\left(\frac{\text{Profit}}{\text{Cost Price}}\right) \times 100$$​​
=> Profit% on the cost price = $$\frac {20x}{80x}$$​ × 100
=> Profit% on the cost price = 25% 
Alternate Solution:
20% profit on Selling Price means Profit = 1 unit and Selling Price = 5 unit 
then, Cost Price = Selling Price - Profit = 5 - 1 = 4 unit 
Profit Percentage on Cost Price =  $$\frac {1}{4} \times 100 = 25\%$$​​