The average daily wage of the 20 workers at a building site is ₹460. Five of them, whose average daily wage is ₹640, are moved to another site. What is the average daily wage of the 15 workers who remain?

The 20 workers cost $20\times 460$ = ₹9,200 a day and the five who leave account for $5\times 640$ = ₹3,200, so the remaining 15 cost 9200 - 3200 = ₹6,000, an average of 6000/15 = ₹400. ₹300 divides the surviving total by the OLD count of 20. ₹460 assumes the average holds even though the best-paid group has gone. ₹550 is the plain midpoint of 460 and 640, which answers nothing here - the group that left was small and well paid, so the rest must sit below ₹460, not between the two figures.