A retailer increase the selling price by 25% due to which his profit percentage increase from 20% to 25%. What is the percentage increase in cost price ?

Explanation:-

100 (Initial CP) ---- 20% ↑(initial profit)---> 120 (SP).
120 (SP) ---25%↑ ---> 150 (New SP).
Let x be the new Cost price.
Selling Price = 150.
x * 1.25 = 150.
x = 120.
% change = [(120 -100)/ 100] *100 = 20%.