Three people go for 30 yuan a night. Each of them paid 10 yuan enough. 30 yuan gave it to the boss. Later, the boss said that 25 yuan was enough for today's discount, so he took out the 5 yuan and asked the waiter to return it to them. The waiter secretly hid 2 yuan's money, and then distributed the rest of 3 yuan's money to three people, each with 1 yuan.

In this way, at the beginning, everyone paid 10 yuan, and now it is returned to 1 yuan, that is, 10- 1 = 9. Everyone only spent 9 yuan's money, three people spent 9 yuan, 3X9=27 yuan+2 yuan hidden by the waiter =29 yuan. Where did the dollar go?

The 9 yuan money spent by each person already includes the 2 yuan hidden by the waiter (that is, the preferential price of 25 yuan+the waiter's possession of 2 yuan =27 yuan =3*9 yuan). Therefore, when calculating the composition of 30 yuan, we should not include the 2 yuan money hidden by the waiter, but should include the 1 yuan returned to everyone. Namely: 3*9+3* 1=30 yuan is just right!

You can also think about it from another angle .. Those three people went out of 30 yuan and spent 25 yuan, and the waiter hid 2 yuan, so each person spent 9 yuan, plus the share of 1 yuan, which happened to be 30 yuan. So this dollar was found.

Interesting math problem:

1, Xiaohua's father can cut off five of his own nails in 1 minute. How many nails can he cut in five minutes?

Xiaohua took 50 yuan's money to the store and bought a car worth 38 yuan, but the salesman only gave him 2 yuan's money. Why?

Xiaojun said, "I went fishing yesterday and caught a tailless fish, two headless fish and three half-baked fish. Guess how many fish I caught? " Students, guess how many fish Xiaojun caught?

Six horses pulled a cart and ran six miles. How many miles did each horse run? How many miles did six horses run at a time?

5. A puppy tied to a tree trunk was greedy for a bone on the ground, but the rope was not long enough, which was 5 cm shorter. How do you teach dogs to scratch bones?

6. Wang walks from place A to place B. 1 minute later, Li walks from place B to place A. When Wang and Li meet on the road, who is farther from A?

7. The clock just struck 13. What should you do now?