Required Mathematical Intelligence

Chapter 50 Four Horses

Horses and donkeys pulling heavy loads can still be seen in the Mexican countryside.Someone pulls four horses A, B, C, and D from village P to village Q.From village P to village Q, A takes 1 hour, B takes 2 hours, C takes 4 hours, and D takes 5 hours.Now I am going to pull away 2 horses at the same time, and ride back 1 horse when I come back. Take 2 horses, and take the time required by the slow-moving horse as the time from P village to Q village.It is said that someone took 1 hours to remove all the horses.Excuse me, in what order did he bring the four horses to Q village?
[Answer: There are two important points when considering this question:
One is that C and D have to go at the same time, because the time required for a slow-moving horse is calculated, and only in this way can it be beneficial to save time.

The second is to ride a fast horse when you come back. C and D are absolutely not acceptable, A is best.

Take this as a principle: the best sequence is:

(1) Take A and B to Q village (2 hours);
(2) Ride on A and return to P village (1 hour);
(3) Take C and D to Q village (5 hours);
(4) Ride on B and return to P village (2 hours);
(5) Finally, bring A and B to Q village. (2 hours), or you can reverse steps 2 and 4. ]
(End of this chapter)