Carol was invited to a Halloween party in an abandoned house. Her friends asked if she was up for a challenge and she said yes.
Soon enough, she was locked inside a room. In this room, there was one door and three light switches next to it.
Behind the door was an empty closet with nothing but a light bulb. Her task was to figure out which switch controls the light bulb.
Inside the closet, she could flip the switches in whatever way she wanted, but once she opened the door, she couldn't touch the switches anymore.
After some minutes of thinking, she was able to get it right. How did Carol do it?
Okay, let's go step by step. She flipped switch number one and waited for a few minutes.
She flipped it again and then immediately flipped switch number two. Then she opened the door and checked the light.
There was no light, so she discovered that it wasn't switch number two that controlled it. So, she decided to touch the bulb to test if it was hot or cold.
If the bulb had been cold, that would have meant that switch number three controlled it. But the bulb was hot, so that meant that switch number one controlled it.
To get back to the party, Carol had to solve another riddle. There was a 7-minute hourglass and a 4-minute hourglass in front of her.
