Aluminium oxide may be electrolysed at ${1000}^{\mathrm{o}}\mathrm{C}$ to furnish aluminium metal (Atomic Mass = 27 amu; 1F = 96,500 C). The cathode reaction is 

${\mathrm{Al}}^{3+}+3{\mathrm{e}}^{-}\to \mathrm{Al}$

To prepare 5.12 kg of aluminium metal by this method would require 

27 g of Al is obtained by passing a current of $3\times 96500\mathrm{C}$.

$\therefore$ 1 g of Al is obtained by passing a current of $3\times \frac{96500}{27}\mathrm{C}$. 

$\therefore 5.12\times {10}^{3}g$ of Al is obtained by passing a current of $3\times \frac{96500}{27}\times 5.12\times 1000$

$=1.83\times {10}^7\mathrm{C}\times 3=5.49\times {10}^7\mathrm{C}$