Marginal PMF of X by summing joint probabilities over all y values — IITM BS previous year questions

Marginal PMF of X by summing joint probabilities over all y values is part of Marginal Distributions, Week 1 in Statistics 2. Prasnya files every IIT Madras BS previous year question from this subtopic here, each one with a worked explanation. Take the whole set as a timed mock and you get accuracy, pacing and per-question analysis back.