Four friends A, B, C, D need to cross a bridge

Answer of the whatsapp puzzle Four friends A, B, C, D need to cross a bridge is : 17 Minutes

How : We need to find out the minimum time required by them to cross the bridge. Key point over here is that “A pair must walk together at the speed of slower person”. Keeping that in mind below would be the steps to get minimum time.

1. A and B will walk together and the time they will take is : 2 minutes  (time taken by B)
2. Now A will return back, since they need lamp, so again time taken by A : 1 minute
3. Now C and D will walk together and join B, they will take 10 minutes to cross (time taken by D)
4. Now B will come back with lamp and he will take 2 minutes
5. Finally A and B will cross the bridge in 2 minutes (time taken by B)

If we accrue these all, we will have total 17 minutes