Four boys Adnan, Balram, Charanpreet and Daniel need to cross a bridge in 17 minutes. Only a maximum of two people can cross the bridge at a time and since it is dark, the boy or boys crossing the bridge should necessarily carry a torch. However, there is only torch with the group. Also, each boy walks with a different speed. Adnan takes 10 min to cross the bridge, Balram takes 5 min, Charanpreet takes 2 min and Daniel takes 1 min. How do they cross the bridge?

Question

anonymous · Answer

Initially, everyone is on this side of the bridge: ABCD /
C&D cross together: 2 mins                              AB     / CD
D comes back with torch: 1 min                       ABD   / C
A&B cross together: 10 mins                             D      / ABC   
C comes back with torch: 2 mins                       DC    / AB
C&D cross together: 2 mins                                       / ABCD

Total time = 17 minutes!