∵ We have to prepare maximum volume solution of 3N. (3N is same as 3M for HCl) Hence we will take all 500 ml of 2N solution and x ml of 5N solution. ∴ 500 × 2 + x × 5 = 3 (x + 500) 1000 + 5x = 3x + 1500 2x = 500 x = 250 ml ∴ Final volume = 500 + x = 500 + 250 = 750 ml