Question

Cate e aranjament de x luate câte 5=5 aranjamente de x luate câte 4?

Answer 1

         
$A_{x}^{5} = 5A_{x}^{4} \\ x(x-1)(x-2)(x-3)(x-4) = 5x(x-1)(x-2)(x-3) \\ \\ \frac{x(x-1)(x-2)(x-3)(x-4)}{x(x-1)(x-2)(x-3)} =5 \\ \\ (x-4)=5 \\ \\ x=5+4=\boxed{9}$