Đố Vui: The Three Switches

Downstairs in a house are three identical on-off switches. One of them controls the lamp in the attic. The puzzle is to work out which switch controls the lamp.

The rules are as follows. You are allowed to manipulate the switches all you like, and then you are allowed only one trip to the attic. How do you do it?

Let’s simplify the question.

If there were only two switches, A and B, the solution is trivial. We switch A on and B off. We head to the attic. If the lamp is on, A is the correct switch, and if the light is off, it’s B.

It gets tough with three switches, A, B and C. What are the possible combinations?

1.All switches off, or all switches on.

2.One switch on, two off.

3.Two switches on, one off.

None of these combinations provide us with a solution, since there is no way to distinguish between two switches in the same position.

It looks like we are stuck?


The solution is as follows:

Switch on A and B for a minute, and then switch off B.

Go to the attic.

If the lamp is on, A is the answer. If the lamp is off but warm, it’s B, and if it is off and cold, it’s C.


Bàn lọan: các bố già K1 nhớ thời mình thực tập "đập đập, vỗ vỗ, lắc lắc" ? Bác nào còn nhớ thì chắc đã tìm ra giải đáp rồi !