Bulb in the Next Room

Qs –

There are 3 switches in a room, where one of them is assigned for a bulb in the next room.
You can’t see whether the bulb is on or off until you leave the room.

Find the minimum number of times you have to go into the room to identify which switch corresponds to the bulb in the other room.

Solution :

The person has to initially turn on the first switch and keep it on for 2-3 minutes.

Next, turn off the first switch and turn on the second one. Go and check to the other room as soon as you turn on the second switch.

If the bulb is glowing, the second switch corresponds to the light bulb.


However, if the bulb doesn’t glow, but touching it feels warm, the first switch is the one that turns the bulb on.

If it’s neither lit nor warm, then the third switch is the desired switch.

So, a person must go only once to the other room to find out the accurate switch.