Riddles are puzzles that test your logic, creativity and lateral thinking skills. Some riddles are so hard that they have remained unsolved for centuries, while others are so clever that they can stump even the smartest minds. Here are some of the most challenging riddles in the world and their solutions.

### 1. The Monty Hall Problem

This is a famous probability puzzle based on a game show scenario. You are given three doors, behind one of which is a car and behind the other two are goats. You pick a door, say Door A, and the host, who knows what’s behind the doors, opens another door, say Door B, which has a goat. He then asks you if you want to switch your choice to the remaining door, Door C. Should you switch or stick with your original choice?

The answer is that you should switch. The probability of winning the car is 2/3 if you switch and 1/3 if you don’t. This is because when you first pick a door, you have a 1/3 chance of picking the car and a 2/3 chance of picking a goat. When the host opens a door with a goat, he eliminates one of the wrong choices, so the remaining door has a 2/3 chance of having the car.

### 2. The Missing Dollar

This is a classic math puzzle that involves some tricky arithmetic. Three friends go to a hotel and rent a room for $30. They each pay $10 and go to their room. Later, the manager realizes that he overcharged them by $5 and sends the bellboy to return the money. The bellboy decides to keep $2 for himself and gives $1 to each of the friends. So now each friend paid $9 for the room, which adds up to $27. The bellboy has $2, which adds up to $29. Where is the missing dollar?

The answer is that there is no missing dollar. The mistake is in adding the $2 to the $27 instead of subtracting it. The friends paid $27 in total, which includes the $25 for the room and the $2 for the bellboy. The remaining $3 were returned to them.

### 3. The Riddle of the Sphinx

This is an ancient riddle from Greek mythology that was posed by the Sphinx, a creature with the head of a woman and the body of a lion, to anyone who wanted to enter the city of Thebes. If they answered correctly, they could pass; if they answered wrongly, they were devoured by the Sphinx. The riddle is:

What walks on four legs in the morning, two legs at noon and three legs in the evening?

The answer is: A human being. A human crawls on all fours as a baby, walks on two legs as an adult and uses a cane as an old person.

### 4. The Prisoners and Hats

This is a logic puzzle that involves four prisoners who are lined up on some steps and are all facing in the same direction. A wall separates the fourth prisoner from the other three. They are all wearing hats, either black or white, but they don’t know what color they are wearing. They are told that there are two black hats and two white hats among them, and that if one of them can guess their own hat color correctly, they will all be freed; otherwise they will all be executed. They are not allowed to communicate with each other or turn around to see behind them. Who can guess their hat color and how?

**The answer is**: The third prisoner can guess their hat color correctly. They can reason as follows: If both the first and second prisoners are wearing black hats, then the fourth prisoner would see two black hats in front of them and would know that they are wearing a white hat. But since they don’t say anything, it means that there is at least one white hat among the first and second prisoners. Now, if the first prisoner is wearing a white hat, then the second prisoner would see a white hat in front of them and would know that they are wearing a black hat. But since they don’t say anything either, it means that both the first and second prisoners are wearing white hats. Therefore, the third prisoner can conclude that they are wearing a black hat.

### 5. The Two Guards

This is another logic puzzle that involves two guards who are guarding two doors: one leads to heaven and one leads to hell. You want to go to heaven but you don’t know which door is which. You can ask one guard one question but you don’t know which guard is lying and which is telling the truth. What question can you ask to find out the correct door?

**The answer is**: You can ask either guard: “If I asked the other guard which door leads to heaven, what would they say?” Then you take the opposite door of what they tell you. This is because if you ask the truthful guard, they will tell you what the lying guard would say, which is the wrong door. If you ask the lying guard, they will lie about what the truthful guard would say, which is also the wrong door.

### 6. The Three Light Bulbs

This is a puzzle that involves some lateral thinking and experimentation. You are in a room with three light switches, each of which controls one of three light bulbs in another room. You can only enter the other room once, and you can’t see the light bulbs from where you are. How can you figure out which switch controls which light bulb?

The answer is: You can turn on the first switch and leave it on for a few minutes, then turn it off and turn on the second switch. Then you enter the other room and check the light bulbs. The one that is on is controlled by the second switch, the one that is off but warm is controlled by the first switch, and the one that is off and cold is controlled by the third switch.

### 7. The Bridge Crossing

This is a puzzle that involves some time management and teamwork. Four people need to cross a bridge at night. They only have one flashlight and the bridge can only hold two people at a time. The flashlight must be used when crossing the bridge. The four people have different walking speeds: A can cross in 1 minute, B in 2 minutes, C in 5 minutes and D in 10 minutes. When two people cross together, they walk at the speed of the slower person. What is the fastest way for them to cross the bridge?

The answer is: The fastest way for them to cross the bridge is in 17 minutes. They can do it as follows:

- A and B cross together (2 minutes)
- A comes back with the flashlight (1 minute)
- C and D cross together (10 minutes)
- B comes back with the flashlight (2 minutes)
- A and B cross together again (2 minutes)

### 8. The Blue-Eyed Islanders

This is a puzzle that involves some logic and induction. There are 100 people living on an island, each of whom has either blue or brown eyes. They are not allowed to communicate with each other or see their own reflection. They know that there are at least one blue-eyed person among them, but they don’t know how many. There is a rule that if a person ever finds out their own eye color, they must leave the island at midnight on the same day. One day, a visitor comes to the island and announces to everyone that they see someone with blue eyes. What happens next?

The answer is: After 100 days, all the blue-eyed people leave the island. This is because they can reason as follows:

- If there is only one blue-eyed person on the island, they will see that everyone else has brown eyes and will realize that they are the only one with blue eyes. They will leave on the first night.
- If there are two blue-eyed people on the island, they will each see one other person with blue eyes and will wait for them to leave on the first night. But when they don’t, they will realize that there must be two blue-eyed people on the island and that they are one of them. They will both leave on the second night.
- If there are three blue-eyed people on the island, they will each see two other people with blue eyes and will wait for them to leave on the second night. But when they don’t, they will realize that there must be three blue-eyed people on the island and that they are one of them. They will all leave on the third night.
- And so on, until all 100 blue-eyed people leave on the 100th night.

### 9. The Green-Eyed Dragons

This is a variation of the previous puzzle, but with a twist. There are 100 green-eyed dragons living on an island, each of whom has either green or yellow eyes. They are not allowed to communicate with each other or see their own reflection. They know that there are at least one green-eyed dragon among them, but they don’t know how many. There is a rule that if a dragon ever finds out their own eye color, they must breathe fire at noon on the same day. One day, a wizard comes to the island and casts a spell that makes all dragons fall asleep for an hour at noon every day. He then announces to everyone that he sees someone with green eyes before leaving. What happens next?

The answer is: Nothing happens. No dragon ever breathes fire because no dragon ever finds out their own eye color

### 10. The Three Gods

This is a puzzle that involves some logic and deduction. You are in a room with three gods, each of whom can only answer yes or no questions. One of them always tells the truth, one of them always lies and one of them sometimes tells the truth and sometimes lies. They are named A, B and C, but you don’t know which is which. You can ask three questions to any of them, but you can’t ask the same question twice. How can you find out their names and their natures?

The answer is: You can ask the following questions:

- Ask A: “If I asked you ‘Are you the liar?’, would you say yes?” If A says yes, then A is the liar. If A says no, then A is either the truth-teller or the random god.
- Ask B: “If I asked A ‘Are you the random god?’, would they say yes?” If B says yes, then B is either the truth-teller or the liar, and A is either the liar or the random god. If B says no, then B is either the truth-teller or the random god, and A is either the truth-teller or the liar.
- Ask C: “If I asked B ‘Are you the truth-teller?’, would they say yes?” If C says yes, then C is either the truth-teller or the liar, and B is either the liar or the truth-teller. If C says no, then C is either the truth-teller or the random god, and B is either the liar or the random god.

.Think you Complete the reading.