Where is Rupee 1??

Ok.. So Herez an interesting one for you to find out..

Three friends went to a hotel.the bill was Rs 75/-
each one contributed Rs.25/-.
the waiter took the bill to the cashier.
the cashier was happy & decided to give them a discount of Rs.5/- & said the waiter to return them Rs.5/-.
but he was confused how to distribute Rs 5 among 3 persons.
he kept Rs 2 in his pocket & gave one rupee to each one of the 3 persons.
so 1st each one contributed 25 Rs now as they are given 1 rupee back their contibution reduces to Rs 24.
they all contributed rs 24 that is 24x3=72 & 2 rupees are in the waiters pocket.
the total becomes 74 but they paid rs 75.
where is the remaining 1 rupee?