Solution of Bridge crossing Riddle

Solution:
-> 1. + 2. - 2 min
<- 1. - 1 min
-> 3. + 4. - 9 min
<- 2. - 2 min
-> 1. + 2. - 2 min

Total - 16 min
note:
-> forward direction
<- Reverse direction

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Bridge crossing Riddle

Question:
There are four people at the end of bridge. They take following time to cross the bridge:
1st: 1 min
2nd: 2 min
3rd: 7 min
4th: 9 min

Condition: 
1. They have only one torch and they can't cross bridge without torch.
2. and only 2 person can cross bridge at a time.

Solution of Burn the rope....good puzzle

Solution:
Take 2 ropes R1, R2. Light R1 at both ends and R2 at one end. When R1 is completely burned (30 minutes have passed), light R2 at the other end. When R2 is completely burned 45 minutes have passed.

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Burn the rope....good puzzle

Question:
there are unlimited ropes of same length and if we burn them it will take 1 hour.
How to measure 45 mins?

Flying bird from trains puzzle(Bumblebee)

Question: 
Two trains enter a tunnel 200 miles long (yeah, its a big tunnel) travelling at 100 mph at the same time from opposite directions. as soon as they enter the tunnel a supersonic bee flying at 1000 mph starts from one train and heads toward the other one.
as soon as it reaches the other one it turns around and heads back toward the first, going back and forth between the trains until the trains collide in a fiery explosion in the middle of the tunnel (the bee survives). how far did the bee travel?

Bridge Crossing in minimum time

Problem Statement:

Four people need to cross a rickety rope bridge to get back to their camp at night. Unfortunately, they only have one flashlight and it only has enough light left for seventeen minutes. The bridge is too dangerous to cross without a flashlight, and it’s only strong enough to support two people at any given time.

Each of the campers walks at a different speed. One can cross the bridge in 1 minute, another in 2 minutes, the third in 5 minutes, and the slow poke takes 10 minutes to cross. How do the campers make it across in 17 minutes?

Solution:

To get everyone across in 17 minutes, we need get the two slowest people across together; otherwise we are wasting too much time. Once we get them across, how do we not make one of them walk back with the flashlight?