Sum of marks in the 1st, 2nd, 3rd and 4th examinations = (59 × 4) = 236 …(1) Sum of marks in the 2nd, 3rd 4th and 5th examinations = 61 × 4 = 246 …(2) Subtracting (1) from (2) we get: Marks of the 5th examination - Marks of 1st examination = 10 Let the marks of first and fifth examination be 8x and 9x respectively. Then, 9x - 8x = 10 x = 10 ∴ Marks of fifth examination = 9x = 9 × 10 = 90