1. The Two Doors
Puzzles : You are in a room with two doors: one leads to freedom and the other to death. There are two guards, one always tells the truth and the other always lies. You can ask one guard one question. What do you ask?
Answer: Ask either guard, "If I were to ask the other guard which door leads to freedom, what would he say?" Then choose the opposite door. This works because the truthful guard would point to the door that leads to death, while the lying guard would do the same.
2. The Light Switches
Puzzles : You have three light switches outside a room, and you need to determine which one controls a single light bulb inside. You can only enter the room once. What do you do?
Answer: Turn on the first switch for a few minutes, then turn it off. Turn on the second switch and enter the room. The light bulb that is on is controlled by the second switch, the one that is off but warm is controlled by the first switch, and the cold one by the third switch.
3. The Fox, Chicken, and Grain
Puzzles : You need to get a fox, a chicken, and a bag of grain across a river. You can only take one at a time, and if you leave the fox alone with the chicken, it will eat it. If you leave the chicken alone with the grain, it will eat it. How do you do it?
Answer: Take the chicken across first. Go back and take the fox across. Leave the fox on the other side but take the chicken back with you. Leave the chicken, take the grain across, and finally go back for the chicken.
4. Three Hats
Puzzles : Three people are wearing hats that are either red or blue. They can see each other’s hats but not their own. The first person says, "I don't know what color my hat is." The second person also says the same. The third person then confidently states the color of their hat. What color is it?
Answer: The third person's hat is red. If the first person saw two blue hats, they would know their hat was red. Since they don't know, there must be at least one red hat. The same logic applies to the second person, leading the third person to deduce that they must be wearing a red hat.
5. The River Crossing
Puzzles : There are five people who need to cross a river with only one boat that can carry two people at a time. They all have different crossing times. How do they all get across in the least time?
Answer: This problem requires careful planning based on the crossing times. Typically, you would start with the two fastest crossing, one returning, then the two slowest crossing, and then the faster ones again to bring the boat back.
6. The Hourglass
Puzzles: You have a 7-minute and a 11-minute hourglass. How can you measure 15 minutes?
Answer: Start both hourglasses at the same time. When the 7-minute hourglass runs out, flip it. When the 11-minute hourglass runs out, flip it. When the 7-minute hourglass runs out again, flip it. After 4 minutes, the 11-minute hourglass will have 1 minute left. When it runs out, you have measured 15 minutes.
7. The Siblings
Puzzles : A man has two children. One of them is a boy. What is the probability that the other child is also a boy?
Answer: The probability is 1/3. The combinations of two children are: boy-boy, boy-girl, girl-boy. Since one child is a boy, the other child can only be boy in one of the three scenarios.
8. The Weighing Scale
Puzzles : You have 8 balls, and one of them is slightly heavier. You have a balance scale. What is the minimum number of weighings needed to find the heavier ball?
Answer: You can find it in 2 weighings. First, divide the balls into three groups (3, 3, and 2). Weigh the first two groups. The heavier group contains the heavier ball. Then take that group of 3 and weigh 1 against 1 to find the heavier one.
9. The Seven Coins
Puzzles : You have seven coins, one is fake and weighs less than the others. You have a balance scale. How do you identify the fake coin?
Answer: Weigh 3 coins against 3 coins. If they balance, the fake coin is one of the remaining. If not, take the lighter group of 3 and weigh 1 against 1 to identify the fake one.
10. The Poisoned Wine
Puzzles: You have 1000 bottles of wine, one of which is poisoned. You have 10 prisoners and 24 hours to find out which bottle is poisoned. How do you do it?
Answer: Use binary representation. Assign each bottle a number from 1 to 1000. Each prisoner can taste wine from bottles that correspond to a binary digit. In 24 hours, you can determine which bottle is poisoned based on which prisoners die.
11. The Missing Dollar
Puzzles: Three friends go to a restaurant and order a $30 meal. They split the cost, each paying $10. The waiter realizes there’s a special and gives $5 back. The friends decide to keep $1 each and give $2 as a tip. Now, they paid $9 each for the meal, totaling $27, plus the $2 tip makes $29. Where’s the missing dollar?
Answer: There is no missing dollar. The $27 includes the tip, so adding the tip again is incorrect. The total cost was $30.
12. The Poisonous Chocolate
Puzzles : You have a box of chocolates, and one of them is poisonous. You can give it to a maximum of 10 people, and they will show symptoms in one day. How can you find the poisonous chocolate in one day?
Answer: Number the chocolates. Use binary to assign each chocolate to a person. The results will show which chocolates are poisonous based on who gets sick.
13. The Elevator Riddle
Puzzles : A man lives on the 10th floor of a building. He takes the elevator to the ground floor to leave, but when he returns, he only takes the elevator to the 7th floor and walks the rest of the way. Why?
Answer: The man is short and can only reach the button for the 7th floor.
14. The Train Riddle
Puzzles : A train leaves a station traveling at 60 miles per hour. Another train leaves the same station 30 minutes later traveling at 90 miles per hour. When will the second train catch up to the first?
Answer: The first train has a 30-mile head start. The second train closes the gap at a rate of 30 miles per hour (90 - 60). Therefore, it will take 1 hour for the second train to catch up.
15. The Hat Color Riddle
Puzzles : In a room, three people wear hats that are either red or blue. They can see the other two hats but not their own. If one person deduces their hat color first, what is it likely?
Answer: The person who deduces their color must see two hats of the same color. If they see one red and one blue, they can't be sure.
16. The 12 Eggs
Puzzles : You have 12 eggs, and one is defective and lighter. You can use a balance scale to find the defective egg. What is the minimum number of weighings needed?
Answer: You can find it in 3 weighings. Split the eggs into groups of 4 and weigh them to eliminate groups.
17. The Train and the Tunnel
Puzzles : A train is traveling toward a tunnel at 60 mph. When it enters, it has to pass through it, and another train is coming from the opposite direction at 80 mph. How do you calculate the time until they meet?
Answer: Calculate the distance covered by both trains based on their speeds and the time they are traveling before they meet.
18. The Coin Problem
Puzzles : You have 10 coins, 9 are identical, and one is heavier. You can use a balance scale. How can you identify the heavier coin in 3 weighings?
Answer: Divide the coins into three groups and weigh them strategically to isolate the heavier coin.
19. The Family Riddle
Puzzles : A man is looking at a picture of someone. His friend asks, "Who is it you are looking at?" The man replies, "Brothers and sisters, I have none. But that man's father is my father’s son." Who is the man in the picture?
Answer: The man in the picture is his son.
20. The Crossing River with Wolves and Sheep
Puzzles : You have a wolf, a goat, and a cabbage to transport across a river. You can only take one at a time, and you can't leave the wolf alone with the goat or the goat alone with the cabbage. How do you do it?
Answer: Take the goat across first, go back alone, take the wolf across, bring the goat back, take the cabbage across, and finally bring the goat back across.
