Step two, how long did the rabbit run in 70 minutes?
70= 1+20+2+20+3+20+4.
Explain that the rabbit ran for four paragraphs and rested for three times for 70 minutes. The distance the rabbit runs is
s = 1/3 * 1+ 1/3 * 2+ 1/3 * 3+ 1/3 * 4 = 10/3km。
How far is the rabbit from the finish line? M = 3.5-10/3 =1/6km.
In the third step, when the tortoise reaches the finish line, the rabbit has just finished the fourth section and needs to enter the fourth rest period, that is, rest for 20 minutes, and the fifth section needs to run for 5 minutes. 1/3 * 5 > 1/6 shows that the rabbit has not finished the fifth section for 5 minutes, that is, the finish line. How long did the fifth district run? T = (1/6)/(1/3) =1/2 minutes.
Summary: The tortoise reached the finish line first, and the fourth rest time and the fifth running time of the rabbit happened to be the time behind the tortoise, that is, 20+ 1/2=20. Five minutes.