[DexterQ]

This one problem really puzzles me:

One way to utilize naturally occurring uranium (0.72% ²³⁵U and 99.27% ²³⁸U) as a nuclear fuel is to enrich it (increase its ²³⁵U content) by allowing gaseous UF₆ to effuse through a porous membrane. From the relative rates of effusion of ²³⁵UF₆ and ²³⁸UF₆, find the number of steps needed to produce uranium that is 3 mole % ²³⁵U, the enriched fuel used in many nuclear reactors.

I have no idea where to start from in this problem. What does it mean by "step"? I have done a search for the topic on Wikipedia and a few other pages but still don't understand the process of this.

[Borek]

What would be the enrichment after effusing them through one hole?

If you effuse the enriched gas through second hole, what would be the enrichment?

Each hole is a "step".