Boy sells a book for Rs. 810 he gets a loss of 10 %, To gain 10%, what should be the SP?	Choose the correct option:
A) 430
B) 990
C) 550
D) 590
E) 600

Rationale: "cost price = 810 / 90 x 100 = 900 to gain 10 % = 900 x 10 / 100 = 90 sp = cp + gain = 900 + 90 = 990 answer : b"
Answer: B