Brainteaser answer: Answers to 10 Most Difficult Interview Brainteasers Ever Asked

Brainteaser Answer 3

A Light-bulb Moment!

Answer 3:  First and foremost, for your own reference, name the switches “a, b and c.”


  • Turn on switches a and b.
  • Wait 10 minutes.
  • Turn switch b off.
  • Enter the room.
  • Whichever light bulb is now on, is controlled by switch a (the only one, still on).
  • Feel the other 2 light bulbs (carefully).
  • Whichever light bulb is warm is controlled by switch b.
  • The cold light bulb must be controlled by switch c.

All you have to do is think outside the box!

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