The Odd Light
Four buttons are on a table. Three of them light up when pressed, while turning another button off, and the fourth button turns on when pressed, causing no other effects. Unfortunately, you don't know which light functions differently from the others. What's the maximum number of times you need to turn on a light before you know which light functions differently from the other three?
The answer is 5.
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1 solution
Maximum turn-ons: 5/ 1st turn-on: Turn on by itself no matter what type of bulb it is because there are no other lights that can turn off as a reaction. (First bulb)/ 2nd turn-on: The bulb turns on while another turns off. (Second bulb)/ 3rd turn-on: The bulb turns on while another turns off. (Third bulb)/ 4th turn-on: The bulb turns on, not causing any reactions. (Fourth bulb)/ (Before the fifth turn-on, turn off the first bulb and fourth bulb if they're both on. If only one of those two is on, turn it off. If both are off, you're all set, though the fourth bulb would be on from the fourth turn-on.)/ 5th turn-on: Turn on the first or fourth bulb. If the one you pick changes another bulb, it is the bulb you didn't pick. If the bulb you picked turned on and didn't cause any side effects, it's that bulb./ (I have put the slashes to separate the steps.)