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Puzzle | The Bridge Riddle
• Difficulty Level : Medium
• Last Updated : 17 Sep, 2019

Puzzle:
You are a scientist who works in a lab. You are in the lab and accidentally, you pull the lever with the skull symbol which released the zombies trapped inside the prison of the Lab. The zombies started to come out of prison. You need to get away and safe from them. With you are the janitor, the lab assistant and the old professor who work with you in the lab. So now it’s your responsibility to get them safe as well.

The lab is situated on a distant island which is connected to the land through only an old bridge. You can move across in a minute while the lab assistant takes 2 minutes, the janitor 5 minutes and the professor takes a whole 10 minutes, respectively. As it is so dark you should take a lamp with you to cross the bridge. Unfortunately, the bridge will hold only two persons at a time. By the professor’s calculations, the zombies will reach them in 17 minutes. So you need to get yourself and all others to the other side of the bridge in 17 minutes and cut the rope of the bridge to avoid zombies crossing it. Can you get everyone across and cut the ropes within 17 minutes? If so, how?

Solution:

1. First, you need to go with the fastest one. You and the lab assistant cross the bridge in 2 minutes. 2 minutes have passed
2. You run back to the other side in 1 minute. 3 minutes have passed
3. Next, the professor and the janitor cross the bridge in 10 minutes. Now 13 minutes have passed and there are only 4 minutes left and you are on the wrong side.
4. Now the lab assistant grabs the lamp and return backs to you in 2 minutes. 15 minutes have passed.
5. Now you and the lab assistant make the final crossing in another 2 minutes. 17 minutes have passed.
6. As you step down on the far side you can cut the rope and now you all are safe in 17 minutes.

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