The Challenge
 At the bottom of a stairway are three wall switches. Each one controls one of three working wall sconces (lights) in an upstairs hallway. None of the illumination created by any of the sconces is visible from the bottom of the stairs.
What is the minimum number of visits upstairs needed to verify which switch controls which sconce? Explain your answer.
 The Correct Answer
One (1) visit upstairs.
Start with all switches in the off position. Turn the left switch on. Wait five to ten minutes. Turn off the left switch. Immediately turn on the middle switch. Immediately go upstairs. The light that is on is controlled by the middle switch. The light that is off but has a warm/hot bulb is controlled by the left switch. The light that is off and does not have a warm/hot bulb is controlled by the right switch.
No, there is no one available to send upstairs on your behalf.
No, you can not see the lights from where the switches are.
No, the lights are not (cool) LED lights.
My favorite response:
"I flick the switches from my Mother's basement and yell upstairs to tell me which ones light up. And to heat up the meatloaf."
Thanks, Matt.
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The Winners
The winners of this month's "Mental Gymnastics" challenge are:
- Joseph Dvorak, Womack Machine Supply (Farmers Branch, TX USA) (first respondent to answer correctly)
- Donald Cottrill, Hydro Air Hughes (North Haven, CT USA) (picked at random from all other correct respondents)
- Chad Robinson, Advanced Pneumatics (Fredericksburg, VA USA) (picked at random from all other correct respondents)
- Steven Samaniego, Womack Machine Supply (Farmers Branch, TX USA) (picked at random from all other correct respondents)
- Tony Windsberger, Arrow Tank & Engineering (Coon Rapids, MN USA) (picked at random from all other correct respondents)
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