Which formula requires a custom search formula because it is not allowed by a custom report formula?

The formula that requires a custom search formula because it is not permitted by a custom report formula is to calculate (x+y)/40. This particular formula involves conducting arithmetic operations in a combination that is typically outside the straightforward calculations that standard custom report formulas can handle.

In a custom report, there are limitations on how formulas can be structured primarily due to the need for clarity and ease of use. Many reports focus on simple aggregated values and predefined calculations to ensure that users can derive key metrics without complex adjustments.

In contrast, custom searches offer more flexibility and can accommodate advanced formulations such as (x+y)/40. This capability allows users to derive more complex insights or calculations involving multiple fields and arithmetic operations, which is ideal for nuanced analyses when simple metrics are insufficient.

Other options listed may involve calculations that could be performed within the confines of a standard reporting environment or don't require the level of complexity that necessitates a custom search formula.