1. There are two unevenly distributed incense sticks, and the time for burning them is one hour. What method can you use to determine a period of 15 minutes?

Answer: Light two incense sticks at the same time. The first incense sticks at both ends, and the other incense sticks at only one end. When the first incense sticks out (this is 3/4 of the total length), light the other end of the second incense stick, and the time from ignition to extinction is 15 minutes!

2. A manager has three daughters, and the ages of the three daughters add up to 13, and the ages of the three daughters add up to the manager's own age. A subordinate knows the manager's age, but he still can't determine the ages of the three daughters. At this time, the manager says that only one daughter's hair is black, and then the subordinate knows the ages of the three daughters. What are the ages of the three daughters? Why?

a: the age of the three girls should be 2, 2 and 9. Because only one child has black hair, that is, only she has grown up, and the other two are still young, that is, less than 3 years old, with light hair. The recombination manager should be at least 25 years old.

3. There are 1 sweets in the teacher's box, and there are just 1 students.

The teacher said, each of you should be given a candy, and there is still one left in the box. How to divide it?

A: Everyone should be given a candy, and the last one should be given to one person together with the box.

4. There are two blind people. They both bought two pairs of black socks and two pairs of white socks. Two blind people accidentally mixed up eight pairs of socks. How can each of them get back two pairs of black socks and two pairs of white socks?

a: each pair of socks was unpacked, each person took one, and there were no left and right socks. Finally, two pairs of black socks and two pairs of white socks were taken back.

5. A train leaves Los Angeles for new york at a speed of 15 kilometers per hour, and another train leaves new york for Los Angeles at a speed of 2 kilometers per hour. If a bird starts with two trains at a speed of 3 kilometers per hour, starts from Los Angeles, meets another train and returns, and flies back and forth in turn until the two trains meet, how long does the bird fly?

a: convert the flying distance of birds into time calculation. Let the distance between L.A. and new york be a, the time when the two trains meet is a/(15+2)=a/25, and the flying speed of the bird is 3, then the flying distance of the bird is a/25*3=6/5a.

6. You have two cans, 5 red marbles and 5 blue marbles, and you can put them by yourself according to the envisaged method. What is the exact probability of getting the red ball in your plan?

A: The probability of putting one red ball in one jar and 49 red balls and 5 blue balls in another jar is close to 75%.

This is the maximum probability that can be achieved.

in fact, as long as a jar is put <; 5 red balls, no basketball,

the probability of taking out the red balls is greater than 5% if you put the remaining balls in another jar

7. You have four jars containing pills, each of which has a certain weight, and the contaminated pills are the uncontaminated weight+1. Weigh only once, how to judge which jar is contaminated?

Answer: Take 1 pill from No.1 can, 2 pills from No.2 can, 3 pills from No.3 can and 4 pills from No.4 can. Weigh the 1 pills. If they are heavier than the normal weight, the number of cans is faulty.

8. Xiaoming and Xiaohua bought 1 Jin of honey and put it in a big bottle. To divide the honey equally, there are only two empty bottles, one of which is exactly 7 Jin and the other is exactly 3 Jin. How can we separate the honey by the simplest method? Remember to use the simplest method, that is, the method with the least number of times.

answer: 1 kg bottle, 7 kg bottle and 3 kg bottle

1.37

2.343

3.64

4.613

5.91

6.91

7 before the start.

9. For a batch of lamps numbered from 1 to 1, all the switches are turned up (on), do the following: dial the switch in the opposite direction for every multiple of 1; A multiple of 2 dials the switch again in the opposite direction; A multiple of 3 turns the switch again in the opposite direction ... Q: Finally, the number of the light in the off state.

a: when the square root of the number is an integer (that is, a complete square number), it faces down, and the others face up.

In this way, No.1, No.4, No.9, No.16, No.25, No.36, No.49, No.64, No.81 and No.1 are facing down

1, three hunters are crossing the river with a black bear and two brown bears.

The boat is very small, and can only carry two people, or two bears, or one bear and three bears at a time. Bears will eat people

How can we cross the river safely

A: The black bear first transports a brown bear across the river, and when he comes back from rowing, he transports another brown bear across the river. When he comes back from rowing, two tearful people row across the river, a hunter brings back a brown bear, a hunter transports the black bear across the river, a hunter brings back a brown bear, two hunters row across the river, and the black bear rows back to transport the two brown bears across the river twice < p There are only two kinds of hats in black and white, and there is at least one black one. Everyone can see the color of other people's hats, but not their own. The host first shows everyone what hats others are wearing, and then turns off the lights. If someone thinks they are wearing a black hat, they will slap themselves in the face. The first time I turned off the lights, there was no sound. So I turned on the light again, and everyone watched it again. When I turned off the light, it was still silent. It was not until the lights were turned off for the third time that there was a slap in the face. How many people are wearing black hats?

a: there are three people wearing black hats. Suppose there are n people wearing black, when N=1, black people wearing black clothes will be willing to identify themselves as black when they see that everyone else is white < P >. So the first time you turn off the lights, you should have a sound. It can be concluded that N> 1。 For everyone who wears black, he can see N-1 black hat and assume that he is white. But after waiting for N-1 times and no one has hit himself, every black man can know that he is black. So when the lights are turned off for the nth time, n people beat themselves.

12. There are 1 boxes of cans, each of which is 2 boxes, and each box weighs 1 catty.

But there is one box, and each box only weighs 9 taels.

Now there is only one scale, and it is only allowed to be weighed once.

[Premise: you can't lift it by hand, look. 1.

Take one box from No.1, two boxes from No.2 ... and ten boxes from No.1. * * There are 55 boxes

Put the boxes taken out on the scale and have a look at the figures. When all 1 boxes are 1 kg per box, the figures of 55 boxes should be 55 kg, but the topic says that there is one box with 9 taels per box, so from the way of taking boxes just now. On the 4th ... 1th, the indicators are 54.8, 54.7, 54.6, 54.5, 54.4, 54.3, 54.2, 54.1, 54. You can tell which one is light by the final weight.

13. 1 yuan paid for a bottle of soda, and after drinking it, two empty bottles were exchanged for one bottle of soda. Q: You have 2 yuan money, how many bottles of soda can you drink at most?

a: 39 bottles, starting with the second bottle, which is equivalent to buying 2 bottles in 1 yuan.

14. In the bazaar, a peasant woman sold her eggs laid by chickens in a basket. A young man on a bicycle accidentally touched her basket, which overturned and broke the eggs. The young man wanted to compensate her for the loss and asked, "How many eggs are there in the basket?" "I don't remember the exact number," replied the peasant woman, "but I know that when I take the eggs out of the basket by two at a time or three at a time, four at a time, five at a time and six at a time, there is always one left in the basket, but when I take them out by seven at a time, there is not one left in the basket.

how many eggs were there in the basket?

a: 31. In this problem, we must first know that the least common multiple of 2, 3, 4, 5 and 6 is 6, so this number is 6x+1, and because this number can be divisible by 7, x=56x+1=31. Of course, if you say 721, it is ok, but in order to consider the actual situation, 31 is more practical.

15. A lady went shopping with two banknotes from 5 yuan, and happened to buy things from 1 yuan. She bought 22 yuan grapes, 11 yuan apples, 3 yuan oranges, 15 yuan peanuts, 14 yuan garlic and 8 yuan washing powder. But this old lady is a freak. She has five shops to buy things. I only hope that one of the shops will give me change, and I don't want to change it. Excuse me, is there such a just thing?

A: There are many answers. The old lady first went to a store to get 39 yuan and 36 yuan (a 2 yuan, a 1 yuan, a 5 yuan and four coins) and (a 2, a 1 yuan, a 5 yuan and a coin) with two apples from 5 yuan and garlic from 14 yuan respectively.

Then she went to a second store to buy grapes with a 2 yuan and two coins. (There is a 2 yuan, two 1 yuan, two 5 yuan and three coins left)

I went to the third store and bought an orange with a 2 yuan and a 1 yuan (there is a 1 yuan, two 5 yuan and three coins left)

I went to the fourth store and bought peanuts with a 1 yuan and a five-yuan note (there is a five-yuan note with three coins left)

I spent the last eight yuan (there is a five-yuan note with three coins left) at the fifth store.

I only found money in the first store and didn't change it. . After shopping in five stores,

16. Three frogs can eat three bugs in three minutes, so how many frogs can eat eighty-one bugs in twenty-seven minutes?

a: nine. Three frogs eat three bugs in three minutes, so they can eat twenty-seven bugs in twenty-seven minutes. Now they need to eat eighty-one, so they can only multiply the number of frogs by three.

17. There are three boxes: red, green and Huang San.

Only one box has a prize. There is a note on each box. There are three sentences written on the three notes, and only one sentence is true.

The red box says: The prize is not in the red box.

The green box says: The prize is not in the green box.

Yellow.

a: the red box, because only the red box has a prize.

18.1 2 3 4 5 6 7 8 9=1

Only addition and subtraction can make these numbers finally equal to 1

Because there are many answers

So who can do this problem with the least addition and subtraction symbols

A: 123+45-67+8-9=1

19. Xiaoming's son. I am the same person as Xiao Ming's son. Then Xiao Ming and I are father and son or mother and child.

2. Xiaoming and I are not the same person. Then I am the wife of Xiaoming's son, and then Xiaoming and I are mother-in-law or daughter-in-law.

2. There are four boats, and the time required for these four boats to row to the other side is different. It takes 1 minute for No.1 boat, 2 minutes for No.2 boat, 5 minutes for No.3 boat and 1 minutes for No.4 boat.

How can we row these four boats to the other side in the shortest time?

[Only one person can row at most two boats at a time, but he must row back. ]

Answer: The first time, the fastest two boats cross the river, the fastest one comes back, the second time, the slowest two boats cross the river, the second one comes back, and then the fastest one crosses the river with the rest, one * * * is 17 minutes

21. E takes 12 seconds, and the five of them only have one lamp, which can only be used for 3 seconds, and the bridge can pass two people at most at a time. Excuse me, how to use this unique wait to let all five people pass in 3 seconds-after two people cross the bridge together, someone must bring the light back to the opposite side of the bridge

A: 29 seconds

B: 3 seconds

A: 1 second

D, E: 12 seconds

B: 3 seconds

A, B. B in the past: 3 seconds

22. There are 7 grams, 2 grams of weights and a balance. How to divide 14 grams of salt

into 5 grams and 9 grams each three times with these items?

answer: the first time: put all the salt in a 2-gram weight box on the balance, and you can get 71 grams and 69 grams.

step 2: put 7 grams of weight box and 69 grams of salt on the balance, and you can get 31 grams and 38 grams.

step 3: put 38 grams of salt on the balance, and you can get 19 grams of salt twice. Finally, 9 grams can be obtained by mixing one part with 71 grams, and 5 grams can be obtained by mixing the rest together. Seeking a book with more connotations and comprehensibility

Yu Qiuyu's prose is good, and many of them are his feelings about visiting at home and abroad, which is very good.

If you like it, books such as Tibetan passwords are also very good.

If you like history, I recommend those things in the Ming Dynasty. What is the history of Yuan Tengfei? What books are better to read by learning SQL?

To be easy to understand, let's first look at what kind of database environment we are going to prepare, Oracle or SqlServer, and the operating habits of SqlServer2 are quite different from those of the later versions. Then find a reference book, find a video tutorial, and learn while watching, at least you will get started quickly. A relatively easy-to-understand book on Chinese studies

The Analects of Confucius

Historical Records? Count it as "national studies"

There are plenty of resources. It is suggested that Zhonghua Book Company annotate it. Although it is not deep, it still needs to be annotated after reading.

I recommend Qian Mu's Popular Speech on China Thought and nan huaijin's book.

nan huaijin's books are easy to understand, humorous in language, and Mr. nan huaijin integrates Chinese and Western cultures, erudite and knowledgeable, and reads them.