In calm water, fishermen always paddle at a speed of 5 miles per hour. When he rowed upstream or downstream, he kept the speed constant. Of course, this is not his speed relative to the river bank. . If the fisherman lost his straw hat at 2 pm, when did he get it back? Since the fisherman rowed five miles after leaving the straw hat, he certainly rowed five miles back to the straw hat. Therefore, he always paddles 10 mile. The fisherman rowed at a speed of 5 miles per hour relative to the river, so he must have rowed 65,438+00 miles in 2 hours. So he found the straw hat that fell into the water at 4 pm.
A plane flies from city A to city B and then returns to city A. In the absence of wind, the average ground speed (relative ground speed) of the whole round-trip flight is 100 mph. Suppose there is a persistent strong wind blowing from city A to city B, if the engine speed of the plane is exactly the same as usual during the whole round-trip flight. . . . . . . Can you explain this seemingly contradictory phenomenon? Mr. White's mistake is that he didn't consider the time taken by the plane at these two speeds. It takes much longer to return against the wind than with the wind. In this way, it takes more time to fly when the ground speed is slow, so the average ground speed of round-trip flight is lower than when there is no wind. The stronger the wind, the more the average ground speed drops. When the wind speed equals or exceeds the speed of the plane, the average ground speed of the round trip flight becomes zero, because the plane can't fly back.
4. Make pheasant (chicken) rabbits in the same cage, with 35 heads and 94 feet. Male rabbit geometry? The solution of the original book is; Let the number of heads be a and the number of feet be b, then b/2-a is the number of rabbits and a-(b/2-a) is the number of pheasants. This solution is really great. When solving this problem, the original book probably adopted the method of equation. Let x be pheasant number and y be rabbit number, then X+Y = B, 2x+4Y = A, and X = A-(B/2-A). According to this set of formulas, it is easy to get the answer to the original question: 12 rabbits, 22 pheasants.
5. A hotel with 80 suites can be fully occupied if we set the daily rent as 160 yuan; And every time the rent goes up in 20 yuan, three guests will be lost. Daily expenses for services, maintenance, etc. Each occupied room is calculated in 40 yuan. Question: How can we set the price to be the most profitable? A: The daily rent is 360 yuan. Although 200 yuan was higher than the full price, we lost 30 guests, but the remaining 50 guests still brought us 360*50= 18000 yuan. After deducting 40*50=2000 yuan for 50 rooms, the daily net profit is 16000 yuan. When the customer is full, the net profit is only 160*80-40*80=9600 yuan.
6. The cube of my age this year is four figures, and the fourth power of my age is six figures. These two numbers just use all the ten digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. How old is Weiner? Answer: Let Wiener's age be X, the cube of 10 is 1000, the cube of 20 is 8000, and the cube of 2 1 is 926 1, which is four digits. The cube of 22 is10648; So 10 =
7. A monkey picked 100 bananas in the forest and piled them up. The monkey's house is 50 meters away from the banana pile. The monkey is going to carry bananas home. He can carry up to 50 bananas at a time. But monkeys are greedy and eat a banana every meter. How many bananas can this monkey take home at most? 25. Recite 50 songs to 25 meters first. At this time, I ate 25 pieces and left 25 pieces. Put them down. Go back and recite the remaining 50. At 25 meters, I ate 25 more, and there are 25 more. Then pick up 25 roots on the ground, one ***50 roots, and continue to walk home, one ***25 meters, eat 25 roots, and then leave 25 roots to go home.
8. Mr. S, Mr. P and Mr. Q, they know that there are 16 playing cards in the desk drawer: hearts A, Q, spades 4, clubs 8, 4, 2, 7, 3 J, K, Q, 5, 4, 6. A, the professor chooses a card from this 16 card and counts the number of this card. At this time, the professor asked Mr. P and Mr. Q: Can you infer what this card is from the known points or colors? So, Mr. S heard the following conversation: Mr. P: I don't know this card.