When the plane flies between the two cities, it takes 4H to follow the wind and 5h to return against the wind. The speed of the plane in the still wind is 360km / h. calculate the wind speed and the distance between the two cities

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• 1. To process a batch of parts, it takes 12 hours for Party A to do it alone, 8 hours for Party B to do it alone, and how many parts are left after Party A and Party B do it together for one hour? We need to do it today
• 2. A cement plant planned to produce a batch of cement in January. In fact, it completed one third of the plan in the first ten days, two fifths of the plan in the middle ten days, and another 26 tons in the last ten days. As a result, it exceeded one sixth of the plan. How many tons of cement are planned to be produced in January?
• 3. There are 480 male and female employees in a shopping mall, of which male employees account for 60% of the total number. Later, male employees transferred some people, and male employees account for 36% of the total number How many people have been transferred
• 4. The number of male workers in a workshop is 25% more than that of female workers. Then: a. the number of female workers is 25% less than that of male workers. B. the number of male workers is 25% of that of female workers C. The number of female workers is 20% less than that of male workers
• 5. In hope primary school, there were 325 boys and girls. In the new semester, there were 25 boys and 5 girls, and the total number of students increased by 16? Sixth grade, don't be too complicated
• 6. The ratio of number a to number B is 2:5, and the ratio of number B to number C is 4:7 fast
• 7. The number a is 4 / 5 of the number B. how much less is the number a than the number B? How much more is the number a than the number B? の, write the formula,
• 8. The sum of a and B is - 2.6, B is - 7.5, how much is B bigger than a? The difference between a and B is - 4 / 3, B is - 1 / 6, what is a Please help me, thank you
• 9. A, B and C make 940 parts at the same time. It takes 5 minutes for a part to be made by a, B and C, which is 25% more than that of B. the time for C to make a part is two fifths less than that of A. how many parts does a, B and C make?
• 10. There were two granaries A and B. in the past, warehouse B stored 1 / 5 less grain than warehouse A. now, 1 / 4 of warehouse A's stock is put into warehouse B, and then 30 tons are transported from warehouse B. at this time, the two granaries stored grain together (don't use equations)
• 11. The fast train and the slow train leave each other from a and B. the fast train starts the whole journey 15 km and 11 km before the slow train starts. When they meet, the slow train runs 27% of the whole journey. It is known that the speed ratio of the fast train and the slow train is 5:4. How many kilometers are there between a and B?
• 12. If you increase the speed by 20%, you can arrive one hour earlier than the original time. If you drive at the original speed of 100 km, you will be able to get there, How many kilometers are there between a and B?
• 13. The weight ratio of the two baskets of apples is 5:3. Take 12 kg out of the basket and put it into the basket. At this time, the apples in the basket B are 8 kg more than those in the basket A. how many kg are the two baskets of apples?
• 14. Double integral, the integrand is Max {(XY), 1}, and the integral region is 0
• 15. Is the positive and negative of double integral related to the positive and negative of integral closed region? For example, if the same integrand is positive, but the closed region is positive In the first quadrant and the fourth quadrant, does the double integral become negative? In addition, is the definite integral also related to the positive and negative of the closed interval? For example, if they are all the same positive integrands, will the closed interval affect the positive and negative of the definite integral on the positive and negative half axes?
• 16. Teaching: the relationship between the value of double integral and the parity of integrand and the parity of integral region D Parity of integrand function with respect to X or Y What does it have to do with the value of the product? Compare this question: On the double integral of D: x ^ 2 * y DXDY D = {(x, y): x ^ 2 + y ^ 2 less than or equal to 2x} It is said that this double integral is equal to zero Why
• 17. ∫∫ x ^ 2 / y ^ 2D σ, where D is surrounded by the curve y = 1 / x, y = x, x = 1, x = 2
• 18. The equation of tangent passing through point P (2,3) leading circle x ^ 2 + y ^ 2-2x + 4Y + 4 = 0 is
• 19. Tangent equation of point P (4, - 2) on circle X & sup2; + Y & sup2; - 2x + 4y-4 = 0
• 20. If the tangent line of circle x ^ 2 + y ^ 2-2x-4y-15 = 0 is made through point P (- 1, - 2), then the equation of tangent line is