Lightbulb puzzle

A

Ancutza

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You have a two-storey house. Upstairs there is a light fitting. Downstairs your have 3 switches one of which activates the bulb in the fitting upstairs. 2 of the switches are duds. You can't see the lightbulb from where you stand at the switches. You need to figure out which is the switch that lights the bulb. You can turn on any number of switches but you can only go upstairs to check the bulb is lit ONCE!

How can you be sure you've identified the switch correctly?
 
Switch A, B and C

Turn on switch A first for 5 mins then turn it off then turn on switch B.

Then go up stairs if the bulb is not switched on then it's not B but if it is hot then it is A if it is neither hot nor on then it is C.

Naturally if it is one of those energy saving bulbs that don't get hot then things get a lot harder.
 
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Correct! You big spoil-sport! Personally I don't think I'm as bright as the lightbulb. I spent 2 days thinking about it before having to have it explained.
 
How about - do it at night - flick the switch & step outside & look up at the window ;) Ya don't need to go upstairs then at all!
 
ninsaga said:
How about - do it at night - flick the switch & step outside & look up at the window ;) Ya don't need to go upstairs then at all!
Click to expand...

Mr Bubbly just said that! Right after he said "if two are duds it doesn't matter, just turn them all on" :rolleyes:

He's normally very good at these.....but he's still thinking!
 
Ancutza said:
You have a two-storey house. Upstairs there is a light fitting. Downstairs your have 3 switches one of which activates the bulb in the fitting upstairs. 2 of the switches are duds. You can't see the lightbulb from where you stand at the switches. You need to figure out which is the switch that lights the bulb. You can turn on any number of switches but you can only go upstairs to check the bulb is lit ONCE!

How can you be sure you've identified the switch correctly?
Click to expand...

More to the point, it sounds like you got the same jerk electrician who worked on my house.
 
Another solution.

Turn on A & B only for 5min. Turn off B. Go up stairs and check.

If light on, then its A
If light off and hot, then its B
If light off and cold, its C.
 
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