回复：转帖一道看似简单的“超超难”智力题

Person 1,2,3 take the car first, while 4,5 walk.

T1 is time takes for the car to travel to the destination and come back to pick up the slowest walker (person 4 at speed of 4m/s).

L1 is the distance walked by person 4 during T1. L2 is the distance traveled by the car during T1

L1 = 4 x T1, L2 = 10 x T1, and L2 = 1000 + (1000 - L1)

10 x T1 = 2000 - 4 x T1

16 x T1 = 2000 ==> T1 = 2000 / 16 = 1000/8 = 125

T2 is the time the car travled after picking up the walkers,

4 x T1 + 10 x T2 = 1000

4 x 125 + 10 x T2 = 1000

500 + 10 x T2 = 1000

10 x T2 = 500 ==> T2 = 50

T = T1 + T2 = 175