in fact , the problem here ist u mentioned rs 2 twice once in the expenses of momo and tipps.expense of momo is 25 and 2 rs tipps make 27 and each of u has 1 rs in pocket.u calculated 9x3=27.this is the sum of money u gave from ur pocket which includes the tipps as well and the remaining 3 is in ur pocket so if u count individually , rs 1 is in ur pocket.check it out , if it isnt there u must have bought orange balls(rs 1 ma 3wata authyou pahile hehe)or lost it lol!!