By selling 80 pens, a trader gains the cost of 20 pens. Find his gain percentage? Answers:
A) 25 %
B) 30 %
C) 35 %
D) 40 %
E) 50 %

Rationale: "let the cp of each pen be rs . 1 . cp of 80 pens = rs . 80 profit = cost of 20 pens = rs . 20 profit % = 20 / 80 * 100 = 25 % answer : a"
Answer: A