A project manager needs a certain number of identical valve housings for a power station project.
He starts with 100 raw items which are made as metal castings. Out of this batch, 15 are found leaking from micro-porosities in a subsequent pressure test. 6 of these housings can be recovered by a special sealing process for raw castings.

The 91 housings are then being machined. After this process step 10 machined castings are found leaking. 3 of these items can also be saved using another sealing process for machined castings.