Interview Question

Intern Interview(Student Candidate) Houston, TX

Brain Teaser: Given a room with 3 light bulbs which have

  their respective three switches (On/Off) outside the room. You don't know which switch corresponds to which light bulb. You can do whatever you want with the switches but you can enter the room only once. How will you find which light switch corresponds to which light bulb?

Interview Answer

2 Answers


Hint 1: Think of what happens when a light bulb glows?

Hint 2: It gets heated

Answer: Switch on one bulb for some time. Then switch on another bulb and go into the room. The bulb which is on and hot is the corresponding to the switch you switched on first. The other glowing bulb corresponds to the switch you switched on second.

Interview Candidate on Oct 21, 2012

Hint 1: Imagine that the room has a door.
Hint 2: Open it.

Answer: flip the switches and observe which one corresponds to which bulb. You don't even need to enter it.

Anonymous on Apr 29, 2013

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