x^2/100 + 2·x/100·(100 - x) = 50
x^2/100 + 2·x/100·100 - 2·x/100·x = 50
x^2/100 + 2·x - 1/50·x^2 = 50
1/100·x^2 + 2·x - 1/50·x^2 = 50
1/100·x^2 + 2·x - 2/100·x^2 = 50
-1/100·x^2 + 2·x - 50 = 0
x^2 - 200·x + 5000 = 0
x = 100 ± √(10000 - 5000)
x = 170.7106781 ∨ x = 29.28932188