By selling 90 pens, a trader gains the cost of 30 pens. Find his gain percentage?
Choices
A) 33.3 % B) 32.3 % C) 31.3 % D) 30.3 % E) 29.3 %

Rationale: "let the cp of each pen be rs . 1 . cp of 90 pens = rs . 90 profit = cost of 30 pens = rs . 30 profit % = 30 / 90 * 100 = 33.3 % answer : a"
Answer: A