Question 20
Let $a$, $b$, $c$ and $d$ be four pairwise distinct real numbers. If $a$ and $b$ are solutions of the equation $x^2 - 10c x - 11d = 0$, and $c$ and $d$ are solutions of the equation $x^2 - 10a x - 11b = 0$, determine the sum $a + b + c + d$.