Brainteaser: How to see the light of refrigerator after the door is closed?

Question

I read about this as a brain teaser in Bain's first-round interview in China office this year.

Really stuck here because I assume the light turns off when you close the door. So you could potentially damage the lighting system and keep it always on - then place a camera inside and connect your cellphone to see the light.

What are some other possible solutions?

Answer 1

Hi Jasmin,

This is a variation on another brainteaser (actually one I was asked 10 years ago for my first job in IT).

The answer is to close the door, let the door stay closed for a while, then open the door and touch the lightbulb. If it's warm, it turned on.

The original brainteaser is with 3 lighbulbs and only being allowed to flip switches 1 time (between opening the door into the room) to see which switch affects which light).

Answer 2

Hi Jasmin,

This is indeed an interesting question which is probably relevant for quite a lot of users, so I am happy to provide my perspective on it:

First of all, it is very unlikely that you this information is up to date. Almost no consulting company uses brain teasers anymore - for obvious reasons.
Still, given your question, you may think of any possibility to measure the light being on from either inside or outside of the refrigerator. Below you may find some examples:
- From the inside: Use some type of photochemical paper that reacts to the light inside of the refrigerator, put a smartphone inside the refrigerator with a timer/ live stream of the inside, measure the heat/ electrical voltage of the light, sit inside the refrigerator (note: please do not actually do this)
- From the outside: Put a hole in the door (though this might destroy the refrigerator)

In case you want a more detailed discussion on how to best approach any type of case study question, please feel free to contact me directly.

I hope this helps,

Hagen

Answer 3

Hello!

That is a variant of the 3 bulbs problem! It´s about seeing if it got warm.

however, these type of brainteasers are extremly weird in consulting tbh, and I wouldn´t worry about them at all anymore.

Hope it helps!

Cheers,

Clara

Answer 4

No respectable company will do a case like that nowaways. I hadn't heard of brain teasers in consulting interviews in 20 years…

Honestly, there's no good answer to a bad question.

But well, I guess you can make a hole in the door, put a camera inside the fridge, you can also get inside the fridge (not a good idea). But if the objective is know if the light is turning on after you close the door, you can simply open the door and touch the light bulb - the temperature will be higher if it was on for a long time.