In your cellar there are three light switches in the OFF position. Each switch controls 1 of 3 light bulbs on floor above. You may move any of the switches but you may only go upstairs to inspect the bulbs one time. How can you determine the switch for each bulb with one inspection??
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Solution:
turn switch 1 on for a while .. about 5 mins or more .. then turn it off.
turn switch 2 on and go inspect
the hot bulb is controlled by switch 1
the lit bulb is controlled by switch 2
the unlit and cold bulb is controlled by switch 3

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