There are three light bulbs in a room, and three light switches outside the room. You are outside, and want to match up which switch goes with which light bulb. You can only travel into the room once, and cannot come back in again. You can do anything you want upon entering the room.

How can you set the situation so that you will know which switch goes with which light bulb?

Scroll down for answer..

... Turn 2 lights on, wait a while, then turn 1 off, walk into the room. You'll be left with 1 light on, 1 light off, and 1 off but still hot

I'd have just left the door open.

..shhh! =p

go into the room, call the janitor, and ask.

Turn two switches on, wait a few minutes and turn one off. Go into the room the bulb that's aglow belongs to the switch that's on, the one that's out but hot belongs to the switch you turned off, the one that's out and cold is the untouched switch.

I'd have just left the door open.

Youve done this before in real life! thats cheating!

I'd have just left the door open.

Youve done this before in real life! thats cheating!

???what's real life?????

I'd have just left the door open.

Youve done this before in real life! thats cheating!

???what's real life?????

dont you remember? getting up at daft o clock inthe morning sittingin a que in ya car with all other robots on m1, workin till 9.30 when someone says ok now all eat and drink tea then work till 12 and get told to eat again etc, just to pay ya bills, thats what i was reffering to, and people still do it!

each to thier own!

I'd have just left the door open.

Youve done this before in real life! thats cheating!

???what's real life?????

dont you remember? getting up at daft o clock inthe morning sittingin a que in ya car with all other robots on m1, workin till 9.30 when someone says ok now all eat and drink tea then work till 12 and get told to eat again etc, just to pay ya bills, thats what i was reffering to, and people still do it!

each to thier own!

A vague and extremely frightening memory of a time and place in this life maybe or the last! I'm sure it was different tho somehow???? .................oh yeah that's it, it was the M4

Nice puzzle with a clever answer! But what do you do if the room is so far away that by the time you get there the bulbs have had time to warm up or cool down? Or if you're running ultra cool bulbs that don't emit enough heat to detect? Or if the lights are so high up that you can't reach them?

Obviously no EEs responded yet because their solution would be quite different:

1. Remove the panels from the switches (using a screwdriver you carry with you in your front pocket).

2. Whip out you handy portable multimeter from your bag and measure the voltage across the switches.

3. Locate circuit breaker box and cut the power.

4. Cut the wires to two of the switches, but leave the third as-is.

5. Locate an appropriate electrical timer in your bag and install it inline at one of the switches, using your wire strippers, soldering iron, and solder that you always carry with you. Set the timer for 5 minutes

6. Locate an appropriate step-up transformer from your bag that will boost the voltage to 1,000 volts and install it inline at the other switch.

7. Go back to the circuit breaker box and restore power.

8. Flip all three switches on, and wait for the sound of a light bulb frying.

9. If excessive sparks and a fire result, pull nearest fire alarm and immediately evacuate the building. If anyone should question you about what happened, deny, deny, deny.

10. Assuming no fire, enter the room and the switch with the step-up transformer corresponds to the light which is not on and has obvious signs of excessive voltage having been applied. The switch with the timer corresponds to the light which will turn off after waiting there for five minutes. And the unaltered switch corresponds to the light that remains on.

Nice puzzle with a clever answer! But what do you do if the room is so far away that by the time you get there the bulbs have had time to warm up or cool down? Or if you're running ultra cool bulbs that don't emit enough heat to detect? Or if the lights are so high up that you can't reach them?

Obviously no EEs responded yet because their solution would be quite different:

1. Remove the panels from the switches (using a screwdriver you carry with you in your front pocket).

2. Whip out you handy portable multimeter from your bag and measure the voltage across the switches.

3. Locate circuit breaker box and cut the power.

4. Cut the wires to two of the switches, but leave the third as-is.

5. Locate an appropriate electrical timer in your bag and install it inline at one of the switches, using your wire strippers, soldering iron, and solder that you always carry with you. Set the timer for 5 minutes

6. Locate an appropriate step-up transformer from your bag that will boost the voltage to 1,000 volts and install it inline at the other switch.

7. Go back to the circuit breaker box and restore power.

8. Flip all three switches on, and wait for the sound of a light bulb frying.

9. If excessive sparks and a fire result, pull nearest fire alarm and immediately evacuate the building. If anyone should question you about what happened, deny, deny, deny.

10. Assuming no fire, enter the room and the switch with the step-up transformer corresponds to the light which is not on and has obvious signs of excessive voltage having been applied. The switch with the timer corresponds to the light which will turn off after waiting there for five minutes. And the unaltered switch corresponds to the light that remains on.

There is always that approach!!!

I'd have just left the door open.

Youve done this before in real life! thats cheating!

is expected behaviour from port supporter