How to Measure 45 minutes using two identical wires? | Puzzles for Interview - Interview Preparation PDF Download

Problem

We have two identical wires that take an hour to burn. We need to measure precisely 45 minutes using these wires and we have matchsticks to help us.

Challenge

The wires burn non-uniformly, which means that they may not burn at the same rate throughout. For instance, one wire may burn its first half in just 10 minutes while the other may take 50 minutes to do the same.

Solution

The key to solving this puzzle is to use matchsticks to ignite the wires. Here's how to do it:

Step 1: Light one end of wire 1 and one end of wire 2.

Step 2: After 30 minutes, wire 1 will have burned out completely. At this point, light the other end of wire 2.

Step 3: After another 15 minutes (total time of 45 minutes), wire 2 will have burned out completely.

Explanation

When we light a matchstick, it takes 60 minutes to burn completely. However, if we light the matchstick from both ends, it will burn in half the time, which is 30 minutes. By lighting wire 1 from both ends, we achieve the same effect as lighting a matchstick from both ends. After 30 minutes, wire 1 will have burned out completely, and we can use the remaining half of wire 2 to measure the remaining 15 minutes.

Conclusion

By using this method, we can accurately measure 45 minutes using two identical wires that take an hour to burn. This puzzle demonstrates the importance of creative thinking and problem-solving skills in finding solutions to complex problems.