Sep 30, 2023
The puzzler this week is not automotive in nature. It is non-automotive, as we say here at Car Talk.
Here it is.
There are two windowless rooms. These rooms are on two different ends of a long curved hallway. Both the rooms have doors. So when you're in one room, you can't see into the hallway or the other room around the corner. At all. So basically, you can't see one room when you are in the other.
In one of the rooms, there are three lamps on a table.
And in the other room, down the curved hallway, there are three light switches.
Each of the three switches in one room controls one of the lamps in the other room, all the way down the hall.
And the puzzler is, with the fewest number of visits from room to room, to figure out which lamp goes with which switch. You can turn on one or more of the switches at a time, but then you have to walk all the way to the other room down the hall to figure out which lamp turned on. And then you have to walk back.
And so the question is, what is the minimum number of trips you can take to know which switch controls which lamp?
So here is the answer. This one was clever. The answer is, that it takes just one trip.
Here is what you do.
You sit in the switch room, and you turn on one of the switches, and you stay there, with it on, for a minute or so. But you don't leave the room.
After a bit, you turn it off. Then, you turn on the next switch, and you immediately run to the lamp room. As fast as you can.
When you get to the lamp room, you can see which one is lit. So you know that the second switch goes with that lamp. But you can also tell which one was previously lit because the light bulb will still be warm. So, then you can tell which one goes with the first switch. And then you know, that the third switch goes with the cold bulb that is not lit up.
So, in that one trip, if you're observant and clever, you can tell which switch goes with which lamp in one trip.
Good one!
