Pipes and cisterns with a draining pipe: net rate = fill − drain

CAT has tested this idea 3 times across 3 papers, from 2017 to 2023. Solve one, and the others are the same method with different numbers or wording, which is why repeated concepts are the most efficient thing to practise.

Question	What it asks	Answer
CAT 2017 Slot 2 · QA Q8	inlet and outlet; time for outlet alone to half-empty	A
CAT 2021 Slot 2 · QA Q21	drain opened an hour or two later; time without drain	C
CAT 2023 Slot 2 · QA Q10	two fill pipes and one drain with time relations	A

Part of Time & Work (34 questions since 2017).