Three friends go to a hotel. The room costs ₹300. They each contribute ₹100. Later, the manager realizes the room was only ₹250, so he sends ₹50 back via the bellboy. The bellboy gives ₹10 to each of the three friends and keeps ₹20 for himself. Now, each friend has paid ₹90 (₹270 total) and the bellboy kept ₹20, which makes ₹290. Where is the missing ₹10?