A man buy a book in Rs50 & sale it Rs70. What is the rate of profit ???  Choose the correct option:
A) 10 %
B) 40 %
C) 30 %
D) 25 %
E) 28 %

Rationale: "cp = 50 sp = 70 profit = 70 - 50 = 20 % = 20 / 50 * 100 = 40 % answer : b"
Answer: B