This is a classic puzzle asked in most of the interview questions. Well there are four persons A,B,C and D. All the four persons takes different times to cross the bridge.
person A :1 minute
person B :2 minutes
person C :5 minutes
person D :10 minutes
There is only one Torch available and it is required in crossing the bridge.Two persons can cross the bridge at the same time but will take the time the of the slower one.For Example : if A and C wants to cross the bridge first they will take 5 minutes. All the four persons can come to the other side in 17 minutes. Can you Explain how?

Well this is possible. the only trick is in realizing that you want to get the two slowest people across together, because otherwise you are wasting too much time. but then once you get them across, how do you not make one of them walk back with the flashlight? well, you just have one of the fast people already there waiting to sprint the flashlight back across.
1. A & B crosses with flash light: 2 mins total time: 2 mins.
2. A comes back with flash light: 1 minute Total = 3 mins
3. C & D crosses with flash light: 10 mins Total=13 mins
4. B comes back with flash light: 2 mins Total=15 mins
5. A & B cross = 2 mins Total=17 mins