Bridge Crossing Riddle: 4 People and 1 Flashlight
Use your logical skills to solve this riddle.
Four people are on one side of the bridge. The bridge will be destroyed by a bomb in 17 minutes. Everyone has to get across to the other side before that. The problem is that it’s dark and so they cannot cross the bridge without a flashlight and they only have one flashlight. Plus the bridge is only big enough for two people to cross at once. The four people walk at different speeds: one of them is so fast that it only takes him 1 minute to cross the bridge, another takes 2 minutes, the third guy takes 5 minutes, the the last takes 10 minutes to cross the bridge. When two people cross the bridge together (sharing the flashlight), they both walk at the slower person’s pace.
Can all the four people get across before the bridge blows up? if yes, then how?
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Solution:
Let us name the people as follows
Person A : The person who takes 1 minute to cross the bridge.
Person B : The person who takes 2 minutes to cross the bridge.
Person C : The person who takes 5 minutes to cross the bridge.
Person D : The person who takes 10 minutes to cross the bridge
Person C and D are the slowest guys, so we have to make them walk together. if they walk together and go first that it self will take 15 minutes, as the 5 minutes guy will have to walk back with the flashlight.
It means they both should walk together and not go first. So here is the best possible solution…
Step 1: A and B go with Flashlight from left to right of the Bridge = 2 min
Step 2: A returns to left side with Flashlight = 1 min
Step 3: C and D go with Flashlight from left to right of the Bridge = 10 min
Step 4: B returns to left side with Flashlight = 2 min
Step 5: A and B go with Flashlight from left to right of the Bridge = 2 min
Therefore, Total time taken = 17 minutes.
if you exchange the 2nd and 4th steps, that will be another solution.