8 * 1 / 4 and 1 / 4 * 8 are calculated in the same way and have the same meaning

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• 1. 4 / 3 times 4 and 4 times 3 / 4 have different meanings, but the calculation method is the same (right or wrong)
• 2. -8-3 + 3 + 1-7, read according to the meaning of sum: () read according to the meaning of operation: ()
• 3. How many bases are there for statistics 1-100
• 4. 1. A passenger car runs on the parallel track at the speed of 30m / s, and a freight car comes face to face on the adjacent parallel track at the speed of 40m / s. what is the speed of the passenger sitting by the window in the passenger car when he sees the freight car passing in front of his eyes? What is the formula of average velocity? Can you explain this sentence, especially the following formula? Combined with speed = relative speed. Formula: same subtraction different addition, positive and negative
• 5. For a car with a mass of 2T, when driving on a straight road, the resistance is always 0.2 times of the gravity. After driving at a constant speed for 2km, the engine is turned off, and then it stops after driving for 55m. It is necessary to explain the work (g = 10N / kg) of the traction force on the car in the whole process
• 6. A physics problem about speed calculation When an earthquake occurs, the vibration of the source propagates outward in the form of S-wave and P-wave. The propagation speed of the two waves in the crust is not the same, about 3.4 km / s and 5.6 km / s respectively. The place directly above the source becomes the epicenter. The first one to reach the ground is the P-wave. At this time, people in the epicenter will feel up and down turbulence, and then the S-wave will come, and they will feel left and right sway, If the time difference between P-wave and S-wave arriving at the epicenter is 2 seconds, how many kilometers is the distance from the source to the epicenter?
• 7. If the maximum pressure that the brick can bear is 882000pa, how high can the brick with a density of 1800kg / m3 build a wall at most?
• 8. When the mass of aluminum block is 50g, 882j heat is released and the temperature is reduced to 12 ℃, the original temperature? Specific heat capacity C = 0.88 * 10 ^ 3j / (kg ·℃) Do you have to set X? Is it OK not to set it up
• 9. How to get 3A = 3B from a = b Give some books to the children (3) class. If everyone gives four books, there are two left. If everyone gives five books, there are five left. How many students are there in the class The second problem is best to solve the equation
• 10. Try to explain how to get 3a-2 = 3b-2 from a = B
• 11. "*" represents a new operation, its meaning is a * b = - A * B - (a + b). Find: (1) 3 * 5; (2) (- 3) * - 5
• 12. A new operation is defined, which requires a * b = (a + b) + [a + (- b)] to find the value of 3 * (- 5)
• 13. "A" denotes a new operation. Its meaning is: a B = (- a) · B - (a + b). Find (3 a 4) a 5
• 14. *A * b = - ab - (a + b) for (- 3) * 5 (- 4) * - 5 Use it quickly
• 15. "*" represents a new operation, its meaning is a * b = - A * B - (a + b), then what is the result of (- 3) * - 5
• 16. From the beginning, what is the number of the thousandth four
• 17. What do the numbers on the bottom of a plastic bottle mean?
• 18. What does the number 7 in the triangle at the bottom of a plastic bottle mean? Is it safe?
• 19. What do the numbers 1 to 7 at the bottom of a plastic bottle mean
• 20. What do the numbers "1-7" on the bottom of plastic bottles represent? What are the notes about these signs?