The 9 yuan money spent by each person already includes the 2 yuan money hidden by the waiter. That is, the preferential price is 25 yuan+the waiter has 2 yuan =27 yuan =3*9 yuan.

When calculating the composition of this 30 yuan, we should not include the 2 yuan money hidden by the waiter, but the 1 yuan money returned to everyone. Namely: 3*9+3* 1=30 yuan is just right!