3 switches and Fan Puzzle

Interview puzzles are a type of brainteaser often used by employers during job interviews to assess a candidate's problem-solving, critical thinking, and logical reasoning abilities. These puzzles typically involve solving a challenging mathematical or logical problem or finding a pattern in a set of information. They are designed to test a candidate's ability to think creatively and outside the box, and to provide insight into how they approach complex challenges. here is a puzzle that is commonly asked in Interviews.

Puzzle Details: Your room has three switches. One of these switches is for a fan in the next room. You cannot see whether the fan is on or off unless you come out of the room. What is the minimum number of times you may go in a room to identify the correct switch in another room?


“I would go only once to the other room to find out the accurate switch for the fan. I would turn on the first switch and keep it on for two-three minutes. Next, I would turn off the first switch and turn on the second one. I would run to the other room as soon as I switched on the second switch.

Here there are three possibilities...

If the fan is running, the second switch is for the fan. If the fan is not running, obviously the second switch is not the right switch,

if the blades are rotating slowly, the first switch corresponds to the fan, it's because the fan will not immediately stop when the switch is turned off, speed will reduce gradually and finally come to stationary and for this It takes time.

If the fan is not running and it is not rotating slowly, that is if the fan is stationary then, the correct switch of the fan is the third one.”

Thus, the minimum number of times you may go in a room to identify the correct switch in another room is just one.

Watch the video for a detailed explanation.

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