Question

There are 4 people who have to cross a stretch of 300 km. They normally run at a speed of 10 kmph. One of them has a bike that travels at 50 kmph. The bike first takes one person alone and crosses the stretch while the other two keep running. Then he comes back without wasting time and picks up another person from the way, drives him across the stretch, and does the same for the last person. How long does this whole process take?

Answer 1

There are 4 people who have to cross a stretch of 300km. they normally runat a speed of 10mk/h. one of them has a bike that travels at 50km/h.
Let A , B, C and D are the name of people.
A has a bike that travels at 50km/h.
time taken to carry person B = 300/50 = 6hrs
in 6 hrs person C runs = 6 × 10 = 60km
so, time taken to meet person C = (300-60)/(50 + 10) = 4hrs
and time taken to carry person C = (300 - 10 × 10)/50 = 4hrs
time taken to meet person D = (300 - 14 × 10)/(50+10)
= 160/60 = 8/3 hrs
time taken to carry person D = 8/3 hrs

so, total time taken = 6 + 4 + 4 + 8/3 + 8/3
= 58/3 hrs