Two ships left the river bank at the same time. One sailed from A to B, and the other sailed from B to A. One sailed faster than the other, so they met at a distance of 500 kilometers. After arriving at the scheduled place, each ship will stop for 15 minutes to let passengers get on and off the ship, and then return. The two ferries meet again at a distance of 100 km from the other side. How wide is this river?
2 Walking time
The office building of a company is in the center of the city, and the home of Winston, the president of the company, is near a small town in the suburbs. After work, he always takes the same suburban train back to town. The town station is far from home. His personal driver always drives from home at the same time and goes to the town station to meet the president. Because trains and buses are punctual, they always arrive at the station at the same time.
Once, the driver left half an hour later than before. Winston arrived at the station and couldn't find his car. He was afraid that his wife would scold him for coming back late, so he walked home along the road. On the way, he met his car coming in lightning speed and immediately waved to stop. After jumping on the bus, he casually scolded the driver and told him to turn around and drive back at once. When I got home, as expected, my wife flew into a rage: "Where have you been fooling around again?" You came back 22 minutes later than usual ... "。
How long did Winston walk?
Pay off the arrears
The loan amounts of the four people are as follows: A Iku borrows from Bell 10 USD; Bell borrowed $20 from Charlie; Charlie borrowed 30 dollars from Dick. Dick borrowed another 40 dollars from Iku. There happened to be four people present and decided to check out. What is the minimum amount of dollars to pay off all the arrears at one time?
A dollar bill
Note: There are several denominations of American currency coins: 1 cent, 5 cents, 1 cent, 25 cents, 50 cents,1dollar.
A small shop has just opened, and there are only three male customers and a female shopkeeper in it. When the three men stood up to pay the bill at the same time, the following happened:
(1) Each of these four people has at least one coin, but none of them is a coin with a face value of 1 cent or 1 dollar.
None of these four men can break any coins.
(3) The family name Lu has to pay the biggest bill, followed by the family name Mo, and the family name Ned has to pay the smallest bill.
(4) No matter how every man pays with the coins in his hand, the female shopkeeper can't get the change.
If these three people exchange coins with each other, everyone can pay his bill without change.
(6) When three people exchanged coins twice, they found that none of the coins in their hands had the same face value as their original coins.
(7) With the further development of things, the following situations appeared again:
(8) After paying the bill, two men left, and the man who stayed bought some candy. The man could have paid with the coins left in his hand, but the woman shopkeeper couldn't exchange the coins she is holding for money. So, the man bought candy with a 1 dollar bill, but now the shopkeeper has to give him all her coins.
Now, please don't worry about how the shopkeeper couldn't find the change that day. Which of the three people bought candy with $65,438+0?
12 children at the birthday party
Today is my 13 birthday. At my birthday party, 12 children got together, including me. Every four children belong to the same family. * * * comes from three different families, A, B and C, including my family. Interestingly, these 12 children are all different in age, and the oldest 13 years old. In other words, among the thirteen numbers from 1 to 13, except one number, all the other numbers represent the age of the child. I add up the ages of children in each family and get the following results:
Family A: The total age is 4 1, including a child aged 12.
Family B: The total age is m, including a five-year-old child.
C family: the total age is 2 1, including a 4-year-old child.
There are only two children in family A, only 1 year old.
Can you answer the following two questions: which family do I belong to-A, B or C? How old are the children in each family?
6 shortest time crossing the bridge problem
In the dark, four travelers came to a narrow bridge without guardrails. If you don't use a flashlight, no one will dare to cross the bridge anyway. Unfortunately, four people only brought flashlights, and the bridge was very narrow, so two people passed at the same time. If you cross the bridge separately, the time required for four people is 1, 2, 5 and 8 minutes respectively; And if two people cross the bridge at the same time, the time needed is the time needed for the slower person to act alone. The question is, how do you design a scheme to minimize time?