B.5.QD.CF:5.2 - Replace an assumed means while retaining two outcomes

A team must reproduce an earlier calculation and use new prices for new calculations. A current file stores the quantity 3 and the price 10, so the earlier result is 30. Tomorrow the price becomes 12 and the new result must be 36.

The proposed practice keeps only one mutable price value. Reproducing the earlier result is taken to require keeping that value at 10; obtaining the new result requires changing it to 12. The conflict depends on that proposed means of recovering the earlier input.

Ask instead: What information and operation reproduce the earlier calculation without freezing the current price? For this case, the calculation is quantity times price. Retaining the input pair (3,10), the multiplication rule and the identity of the earlier calculation supplies its result 30. The current pair (3,12) supplies 36. A versioned input or a retained calculation record can therefore replace the supposed need for one unchanged current value.

The scope matters. This construction suffices for the supplied arithmetic question. If the earlier result used a rounding rule, exchange rate or other input, that contribution must also remain recoverable. A claim about who approved the transaction asks another question and is not established by recomputing 30.

Now change the retained requirements: every copy of the earlier price must be destroyed, and no equivalent information may remain, but the system must later recover that price uniquely. The retained-input proposal violates the deletion requirement. The conflict has not been repaired under these new conditions. The next case isolates why this stronger combination can be impossible.