How did we end up purifying the amount of U235 needed? I saw on another page "General Leslie Groves consulted with lead scientists of the project and agreed to

How did we end up purifying the amount of U235 needed? I saw on another page "General Leslie Groves consulted with lead scientists of the project and agreed to investigate simultaneously four separate methods of separating and purifying the uranium-235: gaseous diffusion, centrifuge, electromagnetic separation and liquid thermal diffusion." Seems like a ton of work.