Total price of 10 Fiction books = 10 × 400 = Rs.4000 Let the number of Comic books be N. Total price of N comic books = N × 550 = Rs.550N ⇒ 4000 + 550N = 500 × (N + 10) ⇒ 4000 + 550N = 500N + 5000 ⇒ N = 20 Number of Comic books = 20 ∴ Required difference = 20 – 10 = 10