engineering intelligence MCQ #255

There are 5 switches, but they are not labelled. Each switch corresponds to one of five lights in a room. Each light is either on or off. You can turn the lights on and off as many times as you want, but you can only enter the room one time to observe the bulbs. How can you figure out which switch corresponds to which light?

engineering intelligence MCQ #255

  1. Question 1

    Q1. There are 5 switches, but they are not labelled. Each switch corresponds to one of five lights in a room. Each light is either on or off. You can turn the lights on and off as many times as you want, but you can only enter the room one time to observe the bulbs. How can you figure out which switch corresponds to which light?

    • A) Turn two switches on for 5 minutes, then turn one off
    • B) Turn one switch on for 5 minutes, then turn it off and turn another on
    • C) Turn two switches on, then turn one off after 5 minutes
    • D) Turn one switch on, then immediately turn it off

    Answer: Turn one switch on for 5 minutes, then turn it off and turn another on

    Explanation: Turn switch 1 to ON for 5 minutes. Then turn it OFF. Turn switch 2 to ON. Now go into the room. The hot bulb corresponds to switch 1, the ON bulb to switch 2, and so on.