You are in a house and there are three light bulbs upstairs, and three light switches down stairs, you can only go upstairs once. How do you know which light switch goes to which light switch? (you can't see up the stairs, and there are no windows to go look through, you can't ask a friend to go turn the light on, and you can't attach a cord to the switches.)
Mathlady
Favorite Answer
Turn on one switch for about 10 minutes.
Turn it off, and turn on another switch, leave it on, and go upstairs.
One bulb should be warm but off, which does with the first switch. One bulb should be on, which goes with the second switch. One bulb should be cold, and go with the switch you didn't use.
Anonymous
you are a clever guy with a good understanding of light bulbs.
you turn on the first light switch, but you don't quite have the energy yet to climb the stairs. So you wait a minute or two. you then turn off the first light switch, turn on the second light switch, and then summon all your energy and climb the stairs. The upstairs light that is on is obviously connected the 2nd light switch. you touch the two upstairs lights that are turned off. you cleverly deduce that the one that is hot to touch is connected to the first light switch (it was just on for a minute or two) , and the one that that's cold to touch is connected to the third switch.
The key to this one is that a light bulb can have 3 states (on, off-cold, off-hot). With only 2 states (on, off), the problem would be impossible.
Anonymous
Turn on one switch. Wait a while (10min or so), then turn that switch off and turn another on, then quickly head to the third floor. If the light is on, then the second switch does it. If the light is off, then check if the bulb is warm. If so, the first switch controls it, otherwise, the third switch controls it.
pebbles0_tmb
Turn on the first switch and wait for several minutes, then turn it off. Then flip on the second switch and head upstairs. The bulb that is off and hot is the first switch the bulb that is off and cold is the third switch and the bulb that is on is the second.
The Chairman Of Jazzy Films
Okay so you turn on the first switch for half an hour, when you go upstairs you turn off the first switch and turn on the second. If the light is on and it is hot, you know it is the first light, if it is on and it is cool, its the second one and if it is off and cool then it is the third one