This one problem is at least 50 years old. Three friends hired a room and paid adv rent as ₹30. After some time the hotel owner thought ₹ 30 is too much for these unemployed and so decided to charge only ₹25. He retuned ₹5 through a servant. The servant on his own thought how can ₹5 be divided by 3 so kept ₹2 with him and returned ₹ 3. So each of the three friends paid Rs 9 toward rent and so total is 9*3=27. With servant taken amount of ₹2 total works out to only ₹27+₹2=₹29. How to account for the missing ₹1?
The Rent paid by each is Rs 9 X 3 =Rs.27 as they got Rs. 3 back. Rs 27 includes Rs 25 as rent and Rs 2 taken by the servant. Rs.27 paid by three people includes Rs 2 taken by the servant. The calculation is: Rent Rs. 25 Taken by the servant Rs. 2 Money given back Rs. 3 Total Rs.30