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Watch a video walkthrough of the famous batteries and flashlight logic puzzle from Presh Talwalkar's Mind Your Decisions Youtube channel.
Video description
This is a famous problem that has been used in technical interviews, and it has even appeared on a Mathematical Olympiad. There are 4 good batteries and 4 bad batteries, and you need to insert 2 good batteries to make a flashlight work. How many tests do you need?
Watch the video: https://www.youtube.com/watch?v=Zm1PUSfUMnE