You want to send a valuable object to a friend securely. You have a box that is large enough to contain the object and the box can be fitted with multiple locks. Both of you also have several locks and their corresponding keys. However, your friend does not have the keys to any of your locks. If you send a key in an unlocked box, there is a danger of theft. How can you send the object securely to your friend?
A boy was at a carnival and went to a booth where a man said to the boy, “If I write your exact weight on this piece of paper, then you have to give me $50 but if I cannot, I will pay you $50.” The boy looks around and sees no scale so he agrees, thinking no matter what the carny writes he’ll just say he weighs more or less. In the end, the boy ended up paying the man $50. How did the man win the bet?
A teacher decides to give a pop quiz one day but all of her students refuse to take the quiz thinking that the teacher will call off the quiz. She can give only one of these students a detention for skipping the quiz. All of the students know each other’s names and if a student knows he/she is getting a detention they take the quiz. How can she threaten her students with the single detention so they all take the quiz?
Two children, who were all tangled up in their reckoning of the days of the week, paused on their way to school to straighten matters out. “When the day after tomorrow is yesterday,” said Priscilla, “then ‘today’ will be as far from Sunday as that day was which was ‘today’ when the day before yesterday was tomorrow!” On which day of the week did they have this conversation?
A collective farm was due to deliver its quota of grain to the state authorities. The management of the Kolkhoz decided the trucks should arrive in the city at exactly 11:00 A.M. If the trucks traveled at 30 miles per hour they would reach the city at ten, an hour early; at 20 miles an hour they would arrive at noon, an hour late. How far is the Kolkhoz from the city, and how fast should the trucks travel to arrive at 11:00 A.M.?
Two mathematicians, Tom and Smith are walking down the street. Tom: I know you have three sons. What are their ages? Smith: The product of their ages is 36. Tom: I can’t tell their ages from that. Smith: Well, the sum of their ages is the same as that address across the street. Tom: I still can’t tell. Smith: The eldest is visiting his grandfather today. Tom: Now I know their ages. Do you know the age of the kids?
A farmer challenges an engineer, a physicist, and a mathematician to fence off the largest amount of area using the least amount of fence. The engineer made his fence in a circle and said it was the most efficient. The physicist made a long line and said that the length was infinite. Then he said that fencing half of the Earth was the best. The mathematician laughed at the others and with his design, beat the others. What did he do?
Two old friends, Jack and Bill, meet after a long time. Jack: Hey, how are you man? Bill: Not bad, got married and I have three kids now. Jack: That’s awesome. How old are they? Bill: The product of their ages is 72 and the sum of their ages is the same as your birth date. Jack: Cool… But I still don’t know. Bill: My eldest kid just started taking piano lessons. Jack: Oh now I get it. How old are Bill’s kids?
Your friend pulls out a perfectly circular table and a sack of quarters, and proposes a game. “We’ll take turns putting a quarter on the table,” he says. “Each quarter must lay flat on the table, and cannot sit on top of any other quarters. The last person to successfully put a quarter on the table wins.” He gives you the choice to go first or second. What should you do, and what should your strategy be to win?
You walk into a dark room in which 100 coins are scattered around on the floor. You are told that 10 of them have “heads” on top, and that 90 have “tails”. Your mission is to separate the coins into two groups such that the amount of coins showing “heads” are equal in each group. You cannot see, feel, smell, taste or hear on which side the coins are. Can you perform the mission in a way that it will always work?
Gypsy, Heather and Miriam went parachuting. They jumped out of the airplane one after the other. This is what we know about their last jump. Sometime before Gypsy, Miriam landed. Gypsy jumped out of the airplane either before or after Heather and Miriam. There were more people who jumped out of the airplane before Miriam than the number of people who landed before Gypsy. In what sequence did the three women jumped out of the airplane?
You are standing in a hallway next to 3 light switches that have been switched off. There is another room down the hallway with 3 light bulbs – all are incandescent light bulbs and each light bulb is operated by one of the switches in the hallway. The door to the room is closed and you cannot see the light bulbs from the hallway. How would you figure out which switch operates which light bulb, if you can enter the room with the light bulbs only once?
A king has 1000 bottles of wine and one has been poisoned. Even a sip of the poisoned wine is enough to kill a person. The king asks the royal jailor to identify the poisoned wine bottle by testing them on the prisoners. It takes up to 24 hours for the poison to take effect. There are unlimited number of prisoners at the jailer’s disposal. What is the minimum number of prisoners the jailer needs to identify the poisoned wine bottle in 24 hours?
A genie transformed Abou, the merchat and his three brothers into animals. He turned one into a pig, one into a donkey, one into a camel, and one into a goat. Ahmed didn’t become a pig, and he wasn’t a goat Sharif wasn’t a camel, and he wasn’t a pig If Ahmed was not a camel, Omar was not a pig Abou didn’t become a goat, and he was not a pig Omar was not a goat nor was he a camel What did each of the brothers become?
A boy was carrying a basket of eggs. He fell down and all the eggs broke. When he went back home without any eggs his mother asked how many he had been carrying altogether in the basket. He was unable to remember. But he was able to recall that when they were counted two at a time one was left, when counted three at a time one was left, when counted four at a time one was left, when counted five at a time none were left. Can you tell how many eggs were broken?
