Trains crossing: relative speed covers the sum of lengths

CAT has tested this idea 3 times across 3 papers, from 2020 to 2021. 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 2021 Slot 1 · QA Q21	opposite directions in 14 s; faster passes lamp post in 12 s	C
CAT 2021 Slot 2 · QA Q5	timing of front and rear ends crossing; length ratio	D
CAT 2020 Slot 1 · QA Q14	train passes two walkers at different speeds	B

Part of Time, Speed & Distance (48 questions since 2017).