Work completed in phases as workers join, leave or slow down

CAT has tested this idea 5 times across 5 papers, from 2018 to 2025. 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 2025 Slot 2 · QA Q12	efficiency ratios 4:2:1; middle worker leaves after 20 days	340
CAT 2019 Slot 2 · QA Q15	second joins after 3 days, third joins later doing 10%	A
CAT 2018 Slot 1 · QA Q8	A alone to half, together 4 days, B finishes last 5%	C
CAT 2021 Slot 3 · QA Q9	second joins two hours late; compare with both from start	D
CAT 2018 Slot 2 · QA Q22	one worker's efficiency drops by 30% midway	C

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