The average of the set of numbers is the quotient when the sum of the numbers is divided by the number of items. Given that Markus' fifth score x, the average is x+5. The equation for solving the fifth score and the arithmetic mean is,
(85 + 92 + 82 + 94 + x) / 5 = x + 5
Further simplifying gives,
(353 + x) / 5 = x + 5
Calculating for the value of x gives x = 82.