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# Which switch turns on the light.

• 20-07-2011 8:22pm
Registered Users Posts: 2,071 ✭✭✭

This is an old one but here goes.

You are in a house with two rooms; a downstairs and an upstairs room.
There are three switches in the downstairs room. A, B and C.
There is a single light in the upstairs room.
Only one of the switches will turn on the light.

How do you determine which switch turns on the light, bearing the following in mind:

* There is no direct line of sight between the two rooms.
* You can only go up once and check if the light is own.
* There are no windows in any of the two rooms.

• Closed Accounts Posts: 214 ✭✭

Flip A and B together, then flip off B.
Go upstairs, if light is on, then obviously the correct switch is A.

If light is off, feel it, and if it is warm, the correct switch is B.

If light is neither on nor warm, then correct switch is C.

• Registered Users Posts: 504 ✭✭✭

Would this not work also??

3 light switches....find which one turns on the downstairs room, which leaves 2.

Switch one of these on – go upstairs….if it is on bingo, if not it is the other.

• Registered Users Posts: 2,071 ✭✭✭

Flip A and B together, then flip off B.
Go upstairs, if light is on, then obviously the correct switch is A.

If light is off, feel it, and if it is warm, the correct switch is B.

If light is neither on nor warm, then correct switch is C.

Correct.