By selling 100 pens, a trader gains the cost of 30 pens. Find his gain percentage?
Choose the correct choice:
A) 30 %
B) 33 %
C) 31 %
D) 32 %
E) 34 %

Rationale: "let the cp of each pen be rs . 1 . cp of 100 pens = rs . 100 profit = cost of 30 pens = rs . 30 profit % = 30 / 100 * 100 = 30 % answer : a"
Answer: A