Mass calculation help needed!

Right so I'm having an absolute mind blank on how to do this question.

What is the percentage yield when 20g of aluminium are produced from 50g of aluminium oxide?
2Al2O3--> 4Al +3O2

- So I know that I need to calculate the theoretical yield of aluminium, and then do actual/theoretical x100 but moles really confuse me.
-Do I do 50/2xmr of the Al3O3 to find the moles and then x2 to get the moles of the 4Al
Or do I divide the no of moles of Al3O2 by 2?

Hi,

You would times the no. moles of Al2O3 (using the 20g, so 20/Mr) by 2 to get moles of Al as the mole ration is 2:4 so 1:2

Al302 mol x2 = theoretical moles of AI produced
Can then convert that into theoretical yield in grams of AI if you like but the calculation can be done in moles as well