A large truck drives from city a to city B at 80km per hour. Half an hour after departure, a car chases the truck at 90km per hour. How many hours after departure can the car catch up with the truck?

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• 1. A batch of fruits are transported from the fruit shop. The weight of apples is 21 kg less than 3 times that of pears. The weight of apples is 49 kg more than 2 times that of pears. How many kg are the pears and apples transported?
• 2. The voltage of sinusoidal current for lighting is 220 V, what are its effective value and peak value?
• 3. If the product of six integers a * b * c * D * e * f = 36, a, B, C, D, e and F are not equal to each other, then a + B + C + D + e + F = () a, 0 B, 4 C, 6 D and 8 are solved
• 4. Given that a, B, C, D, e and F are six mutually unequal integers and a × B × C × D × e × f = 36, then a + B + C + D + e + F = ()
• 5. Find the rule: 4 out of 9, 2 out of 9, 1 out of 9, (), 1 out of 36, (), ()
• 6. Four out of nine, two out of nine, one out of nine, (), one out of 36, () find the law
• 7. Find the rules P1, 4, 13, 40, 121
• 8. Find the rule: 1.5, 4.5, 13.5, (), 121.5 1,5,9,13,…… The tenth number is ()
• 9. Find the rule: 1, 4, 13, 40, 121? I want to write an algebraic expression
• 10. What is the law between the numbers 9, 1, 4, 3, 40121
• 11. It takes two hours for a small car to go from land a to land B, and four hours for a large car to go from land B to land a. the two cars face each other from 8:30 at the same time
• 12. The diameter of a car's outer tire is 9 decimeters, and the wheels roll 400 cycles per minute. How many kilometers does the car advance per hour?
• 13. The speed of the car is 80 km / h, and that of the bus is 45 km / h. (1) after X hours, how many kilometers did the car and bus travel together? (2) after X hours, how many kilometers did the car travel more than the bus?
• 14. A passenger car and a freight car are going from place a to place B. the passenger car takes 8 hours to complete the whole journey, and the train takes 9 hours to complete the whole journey. These two cars go through the whole journey every hour What's the distance? Which car is faster? Hurry up
• 15. When Xiao Hong read a story book, she read 5 / 1 of the total pages on the first day, 15 pages less than the first day on the second day, and 3 / 1 of the total pages in two days, Xiao Hong read a story book. On the first day, she read 5 / 1 of the total pages. On the second day, she read 15 pages less than on the first day. On the second day, she just read 3 / 1 of the total pages. How many pages did she read in the two days?
• 16. A math problem: calculate 24 points The geniuses use 12, 12, 31 to calculate 24 o'clock
• 17. The order of 1, - 1 / 2,1 / 3, - 1 / 4,1 / 5, - 1 / 6... Is as follows First line 1 Second line - 1 / 2 1 / 3 The third line - 1 / 4 1 / 5 - 1 / 6 The fourth line 1 / 7 - 1 / 8 1 / 9 - 1 / 10 The fifth line 1 / 11 - 1 / 12 1 / 13 - 1 / 14 1 / 15 ······ Please write down the process, steps and details of the 10th number calculation from left to right in line 20
• 18. Write a program for me to find the sum of the first 20 items of the following sequence: 2 / 1, 3 / 2, 5 / 3, 8 / 5, 13 / 8, 21 / 13
• 19. Fill in the blanks with the appropriate letters so that each line forms a word, and then fill in the blanks in turn with the appropriate words 1.e( ) ( ) ( )（） 2.（ ）e（ ）（ ）( ) 3.( ) ( )e( )（ ） 4.( ) ( )（ ）e( ) 5.( ) ( ) ( ) ( ) e ( ) 1.Can you get to the music room at ( ）o clock? 2.The students ( ) their lesson at half past eight in the morning. 3.This T-shirt is expensive,that one is( ). 4.I( ）have lunch at home .I like eating outside. 5.Don not ( )to close the door.
• 20. Simple calculation of mathematical problems in primary school Olympiad