Interview Riddles

Interview riddles are famous questions asked during interviews by some big companies like Google, Microsoft, Intel etc.

100 Blue Eyes

On a certain island there are people with assorted eye colors. There are 100 people with blue eyes and 100 people with brown eyes. Since there are no mirrors on this island, no person knows the color of their own eyes.

The people on the island are not allowed to talk or communicate with each other in any way. They are also not aware of the number of blue or brown eyed people on the island. For all they know, they could have red eyes too. But they are allowed to observe other people and keep count of the number of people with a certain eye color. There is a rule that the people on the island have to follow – any person who is sure of their eye color has to leave the island immediately.

One day, a person comes to the island and announces to the people that he sees someone with blue eyes. Everyone knows that the person only speaks the truth. What do you think happens?

Riddle Answer

3 Switches and 1 Light Bulb

You have a set of 3 light switches outside a closed door. One of them controls the incandescent light bulb inside the room. With the door closed from outside the room, you can turn the light switches on or off as many times as you would like.

You can go into the room – one time only – to see the light. You cannot see whether the light is on or off from outside the room, nor can you change the light switches while inside the room.

No one else is in the room to help you. The room has no windows.

Based on the information above, how would you determine which of the three light switches controls the light inside the room?

Riddle Answer