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 ?

Answer: Option A

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 = $$\frac{120-100}{100}\times 100$$     = 20%