Torch and Bridge | Puzzles for Interview - Interview Preparation PDF Download

Introduction

The torch and bridge puzzle is a classic problem that challenges your logical and mathematical skills. In this puzzle, you have to figure out how to get four people across a bridge in the shortest amount of time possible, using only one torch.

Contestants

The four people in this puzzle are A, B, C, and D. Each person has a different speed for crossing the bridge. A takes one minute, B takes two minutes, C takes five minutes, and D takes eight minutes.

Rules

There are some rules that you need to follow in order to solve this puzzle. Firstly, there can only be two people on the bridge at a time. Secondly, when two people cross the bridge together, they must move at the slower person’s pace. Finally, the bridge cannot be crossed without the torch.

Solution

To solve this puzzle, you need to plan out the order in which the people will cross the bridge. Here is the solution:
Step 1: A and B cross the bridge together, with A holding the torch. A comes back to the starting point with the torch, taking three minutes in total.
Step 2: C and D cross the bridge together, with B holding the torch. B comes back to the starting point with the torch, taking ten minutes in total.
Step 3: Finally, A and B cross the bridge together again, with B holding the torch. They arrive at the other side of the bridge in two minutes, taking a total of 15 minutes.

Explanation

The key to solving this puzzle is to minimize the number of times the people have to cross the bridge. In this solution, the fastest people (A and B) cross the bridge first and last, while the slower people (C and D) cross the bridge in the middle. Also, only A and B need to come back to the starting point, as they are the fastest. This reduces the total time to 15 minutes.

Conclusion

The torch and bridge puzzle is a great way to exercise your problem-solving skills and logical thinking. By following the rules and planning out the order, you can solve this puzzle in the shortest amount of time possible.