CGI Interview Question: The light bulb question - how... | Glassdoor

Interview Question

Business Analyst Interview Lebanon, VA

The light bulb question - how do you tell if a light switch

  turns on a light bulb in another room.

Interview Answer

1 Answer


The question is: you have three light switches in one room and three light bulbs in another room(you can't see). You can only have one light switch on at a time, and you can only walk to the room with the bulbs once. How do you tell which light switch goes to which light bulb?

Answer: You turn on one light switch for a few minutes. You turn that off, then flip on another one and walk to the room with the bulbs. The light on obviously goes to the switch that's on, and you feel the bulbs to see which bulb is warm and which is cold. The warm bulb goes to the first switch you left on, and the cold one to the remaining switch.

Matthew Morton on Nov 2, 2012

Add Answers or Comments

To comment on this, Sign In or Sign Up.