![](data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 72 71" width="72"></svg>)
Someone swam the Yangtze River upstream and lost a kettle at a. he swam forward for another 20 minutes before he found out that he had lost the kettle. He immediately returned to search for it. How many minutes did it take him to return to search for it at a distance of 2 kilometers? (return speed unchanged)
Let v be the speed of human and V be the speed of water, then after 20 minutes of swimming, the distance between human and a point is 20 (V-V), the distance between kettle and a point is 20V, when returning, the distance between human and kettle is 20 (V-V) + 20V = 20V, when returning, the speed difference between human and kettle is V + V-V = V, the time to catch up with kettle is 20V △ v = 20 (minutes), a: it took him 20 minutes to return
RELATED INFORMATIONS
- 1. 1 1 1 1 ------ + ------ + ------ + .+ -------------- = 1×2 2×3 3×4 2009×2010 1 1 1 1 ---------- + --------- + ---------- + .+ -----------= 10×16 16×22 22×28 94×100
- 2. In a basketball game, the competition system is one game between two teams, with a total of 45 games, how many basketball teams participate in the game?
- 3. A math problem, I hope to explain it If they start at the same time and meet each other for the first time when B runs 100 meters and the second time when a runs 60 meters short of a lap, how long is the runway
- 4. Given that the area of the quadrilateral enclosed by four straight lines y = kx-3, y = - 1, y = 3 and x = 1 is 12, then the value of K is () A. 1 or - 2b. 2 or - 1C. 3D. 4
- 5. (2007) the function f (x) defined on R is both an odd function and a periodic function, and t is a positive period. If the number of roots of the equation f (x) = 0 on the closed interval [- t, t] is n, then n may be () A. 0B. 1C. 3D. 5
- 6. A mathematical problem, requires detailed explanation A bucket of water is poured out for the first time, one sixth of which is poured out for the second time, one third for the last time, and one fourth for the last time. At this time, the water belt bucket is 20 kg, and the weight of the bucket is 5 kg. How many kg of water are there in the bucket at the beginning? A 50 B 80 C 100 D 36
- 7. Given that f (x) = (m-1) x ^ 2 + 2mx + 1 is even function, then f (x) is in the interval (- 5, - 2) A increasing function B decreasing function
- 8. The page numbers of the first volume and the second volume share a 777 number, and the first volume has seven more pages than the second volume___ Page
- 9. A math problem needs detailed explanation After receiving the money, the waiter remembered that the hotel was doing activities now, the original price was 10 yuan per person, and now the activity price was only 25 yuan for three people. But considering that the remaining 5 yuan was not easy for three people to share, he left 2 yuan for them, and then gave them 1 yuan each, The total price is 9 * 3 + 2 = 29 yuan, but the three of them pay 30 yuan. Where is the remaining 1 yuan?
- 10. It should be 3A = 4b, so a: B = 3:4______ (judge right or wrong)
- 11. Panda accountant of Senli fruit store found that the money was less than 100 yuan when he checked out. After checking, he found that a number on a receipt was polluted, which became ■ 52.72 yuan "At the beginning of the month, 72 people came to buy peaches. Each person bought the same amount of peaches and paid the same amount of money. I wrote a collection note to them collectively, which was accidentally soiled. The number of contaminated peaches was 1, and the sum was 152.72 yuan." Is the weasel right? Why? How much should the money be? Please make it clear
- 12. Given that sina + cosa = m, Sina * cosa = n, then the relationship between M and N is?
- 13. Try to explain that the algebraic formula (x + 1) (x + 2) (x + 3) (x + 4) + 1 is a complete square formula
- 14. Who can help me explain the meaning of these four things? – Dielectric-dielectric – Dielectric-metal – Maxwell’s equations – Radiation
- 15. The meaning of the difference between the purchase and sale of goods or some specific explanations and examples Is there any concrete example of the price difference between purchase and sale~ Please attach the definition of "price difference between purchase and sale of goods"
- 16. The structure of the original urine and urine is (on-line, etc.) in turn A glomerulus and tubule B corpuscle and nephron C renal vesicle and ureter D glomerulus and pelvis
- 17. As shown in the figure is a sketch of the formation of urine: (1) in the figure, ② is______ (2) liquid (3) is______ The liquid is______ The difference between the two liquids is that the liquid does not contain______ (3) in a patient's urine test results, found more red blood cells. If it is kidney disease, you think it may be the mark in the picture______ There was a lesion
- 18. The process and illustration of urine formation
- 19. Help explain the formation and process of urine in detail
- 20. Magnesium nitride electronic type