Atoms to Formula Units: Calculate Al2O3 Moles

[IamMoi]

Homework Statement

A sample of aluminum oxide, Al2O3(s), contains 8.29*10^25 total atoms. Calculate the amount in moles of aluminum oxide in the sample. Hint: This is a two-step problem. Calculate the number of formula units first.

Homework Equations

N=N × N$_{A}$

The Attempt at a Solution

8.29×10$^{25}$ ( 1 atm/ 6.02 × 10$^{23}$)
=1.38× 10 $^{2}$

The question mention that it has two steps but I do not know how..
The correct answer is 27.5 mol ...

 

[SteamKing]

One molecule of aluminum oxide has 2 Al atoms and 3 O atoms. The sample contains 8.29*10^25 atoms, which includes both Al and O. This sample also represents X moles of aluminum oxide. Hint: figure out the proportions of Al and O in aluminum oxide.