Four people need to cross a bridge at night and they have one torch. The bridge can handle the load of only two people at a time. Person A can take 10 minutes, B takes 7 minutes, C takes 2 minutes and D takes 1 minute to cross the bridge. When two people cross the bridge together, they must move at the slower person’s pace. What’s the minimum time taken by four of them to cross the bridge.
Time taken by each person
A – 10 Minutes
B – 7 Minutes
C – 2 Minutes
D – 1 Minutes
So we need to calculate the minimum time taken by four of them to cross the bridge.
i) First C and D will go. D comes back with torch.
ii) A and B will go this time. C comes back with torch.
iii) Now C and D will go.
So the total time taken is
i) 2 (slower pace is 2 in case of C and D) + 1 (Time take by D comes back with torch)
ii) 10 (Slower pace is 10 in case of A and B) + 2
If we add three of them, total minimum time taken is 17 Minutes.