Average changes when members join or leave the group

CAT has tested this idea 6 times across 6 papers, from 2017 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 2023 Slot 3 · QA Q12	D joins: average falls x; E joins: rises 2x	D
CAT 2022 Slot 1 · QA Q20	new students 3 kg heavier raise average by 600 g	D
CAT 2017 Slot 2 · QA Q6	two toddlers leave; average up 2 inches	C
CAT 2019 Slot 1 · QA Q34	excluding Gautam vs excluding Ramesh changes the average	A
CAT 2018 Slot 1 · QA Q5	dropping first 10 or last 10 tests changes average by 1	60
CAT 2025 Slot 2 · QA Q3	averages over first 7, first 8, and days 2 to 9	49

Part of Ratio, Mixtures & Averages (84 questions since 2017).