GATE Computer Science (CS) 2016 Shift 1 Solved Paper

Consider a computer system with ten physical page frames. The system is provided with an access sequence (a₁, a₂,…,a₂₀, a₁, a₂,…,a₂₀), where each a_i is a distinct virtual page number. The difference in the number of page faults between the last-in-first-out page replacement policy and the optimal page replacement policy is ______.