A it takes 800/5= 160 seconds to run once.
Then at this time, A ran (4000/3)/ 160=25/3, that is, 8 laps and 1/3 laps.
The distance from the starting line is 800 * 1/3 = 800/3m.
14, the previous day required 30/ 15=2 hours.
The first 10km took 10/ 10= 1 hour, leaving only 1 hour to cover the next 20km.
The last 20km speed is 20/1= 20km/h.
15, chasing the topic
The speed of A is 80 * 1.25 = 100m/min.
It takes time for two people to meet (400+100)/(100-80) = 25 minutes.
16, like the above problem, is a catch-up problem.
The total distance is the sum of the two car lengths, and the speed is the difference between the two car speeds.
The time is (125+140)/(22-17) = 53 seconds.
17, sound propagation needs 1360/340=4 seconds.
The train traveled 57+4=6 1 sec.
The speed of 1360/6 1 is about 22 meters per second.
18, still caught up with the problem.
Make the train x meters long.
(x+ 1050 * 3)/( 1200- 1050)= 25
The solution is x=600.
19、
20、
2 1,100/4 = 25cm
22、
23、
24. The decomposition is 29 10=2*3*5*97.
According to the meaning of the question, middle school students should be teenagers, so the ranking is 2, the age is 15 and the score is 97.
25、
26. The decomposition is 123=3*4 1. According to the meaning of the title, the number of books and the number of people are integers, so the number of people is 4 1, and each person has three books.