Friday, January 9, 2009

Problem solving: Light bulbs and switches

In a R1 room there are three switches and in another separate room R2 there are three light bulbs. The three switches control the light bulbs, but you cannot see the lights in R2 from R1.

You need to discover what switch controls each bulb, but you can enter in the room R2 only one time.


  1. Hint: do you consider light bulbs as bits?

  2. I discussed this with a friend of mine, he came up with interesting idea:

    Turn all switches OFF
    Wait for an hour or so, then turn ON one of them, let it be in ON position for 20 minutes
    After 20 mins, turn second light ON, continuing to leave first light ON
    2-3 mins post turning On second light, turn all lights off
    Enter room r2... touch each of the bulbs. bulb that is coldest was the one that was never turned ON. so u know which switch controls that bulb. the bulb that is the WARMEST is the one that was ON the longest, so u know that switch and the second one was the one u kept on for the shortest period of time.