During a school lunch break, ten kids are discussing about their holiday jobs. In particular, they would like to know their average monthly salary (for the ten of them), but no one wants to admit openly exactly how much they make. Can you devise a way for them to calculate their average (mean) salary without anyone having to tell anyone else what their individual salaries are?

In an Island the natives lie and visitors speak truth. A man wants to know whether a salesman beside him in a bar is a native or a visitor. He asked him to ask a woman beside him whether she is a native or visitor. He replied, “She says she is a visitor.” Then he was immediately able to determine if the salesman is a native or a visitor. Is the salesman a native or a visitor?

Suppose we lay down two cups in front of you. One of the cups is filled with tea and the other one with coffee. Now we ask you to take a spoonful of tea and mix it with the coffee. At this moment, the coffee cup has a mixture of tea and coffee. You have to take that mixture (spoonful) and add it back to the tea. Can you now tell if the cup of coffee has more tea or the cup of tea has more coffee?

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?

There are 25 horses and you need to figure out the 3 fastest horses by placing them into races. You can race 5 horses at a time. Each horse always finishes the race in the same amount of time and there are no ties. The only information you get from each race is the order that the 5 horses finished in. You will not get any information regarding the time taken for the horses to complete the race. What is the smallest number of races you need to find the 3 fastest horses in order?

Four people need to cross a rickety rope bridge to get back to their camp at night. Unfortunately, they only have one flashlight and it only has enough light left for seventeen minutes. The bridge is too dangerous to cross without a flashlight, and it’s only strong enough to support two people at any given time. Each of the campers walks at a different speed. One can cross the bridge in 1 minute, another in 2 minutes, the third in 5 minutes, and the fourth takes 10 minutes to cross. How do the campers cross the bridge in 17 minutes?

Every man in a village of 100 married couples has cheated on his wife. Every wife in the village instantly knows when a man other than her husband has cheated, but does not know when her own husband has. The village has a law that does not allow for adultery. Any wife who can prove that her husband is unfaithful must kill him that very day. The women of the village would never disobey this law. One day, the queen of the village visits and announces that at least one husband has been unfaithful. Everyone knows that the queen only speaks the truth. What happens?

You are given two eggs, and access to a 100-storey building. Both eggs are identical. The aim is to find out the highest floor from which an egg will not break when dropped from a floor. If an egg is dropped and does not break, it is undamaged and can be dropped again. However, once an egg is broken, it cannot be used anymore. If an egg breaks when dropped from floor N, then it would also have broken from any floor above that. If an egg survives a fall from floor N, then it will also survive any fall below floor N. What is the minimum number of egg drops required to find the solution?

You are on your way to visit your Grandma, who lives at the end of the valley. It’s her anniversary, and you want to give her the cakes you’ve made. Between your house and her house, you have to cross 5 bridges, and as it goes in the land of make believe, there is a troll under every bridge! Each troll, quite rightly, insists that you pay a troll toll. Before you can cross their bridge, you have to give them half of the cakes you are carrying, but as they are kind trolls, they each give you back a single cake. How many cakes do you have to leave home with to make sure that you arrive at Grandma’s with exactly 2 cakes?

A man worked for a high-security institution, and one day he went in to work only to find that he could not log in to his computer terminal. His password wouldn’t work. Then he remembered that the passwords are reset every month for security purposes. So he went to his boss and they had this conversation: Man: “Hey boss, my password is out of date.” Boss: “Yes, that’s right. The password is different, but if you listen carefully you should be able to figure out the new one: It has the same amount of letters as your old password, but only four of the letters are the same.” Man: “Thanks boss.” With that, he went and correctly logged into his station. Can you figure out the old and new passwords?

Your friend has 100 red marbles, 100 blue marbles and 2 jars. He proposes a game. He fills the jars with the marbles, put the two jars behind his back and tell you to pick one of them at random. You’ll then close your eyes, he’ll hand you the jar you picked, and you’ll pick a random marble from that jar. You win if the marble you pick is blue, and you lose otherwise. To give you the best shot at winning, your friend gives you the two jars before the game starts and says you can move the marbles around however you’d like, as long as all 200 marbles are in one of the 2 jars (that is, you can’t throw any marbles away). How should you move the marbles around to give yourself the best chance of picking a blue marble?

The court takes decision to relax the sentence given to criminal if he can solve a puzzle. Criminal has to take decision to open one of the doors. Behind each door is either a lady or a tiger. They may be both tigers, both ladies or one of each. If the criminal opens a door to find a lady he will marry her and if he opens a door to find a tiger he will be eaten alive. Of course, the criminal would prefer to be married than eaten alive. Each of the doors has a statement written on it. The statement on door one says, “In this room there is a lady, and in the other room there is a tiger.” The statement on door two says,”In one of these rooms there is a lady, and in one of these rooms there is a tiger.” The criminal is informed that one of the statements is true and one is false. Which door should the criminal open?

On a certain island there are people with assorted eye colors. There are 100 people with blue eyes and 100 people with brown eyes. Since there are no mirrors on this island, no person knows the color of their own eyes. The people on the island are not allowed to talk or communicate with each other in any way. They are also not aware of the number of blue or brown eyed people on the island. For all they know, they could have red eyes too. But they are allowed to observe other people and keep count of the number of people with a certain eye color. There is a rule that the people on the island have to follow – any person who is sure of their eye color has to leave the island immediately. One day, a person comes to the island and announces to the people that he sees someone with blue eyes. Everyone knows that the person only speaks the truth. What do you think happens?

Five potential donors are sitting on a bench from left to right outside the surgery room and are waiting for the doctor. Their ages are 6, 10, 31, 47 and 61. Their heights are 41, 49, 61, 66 and 75 inches. Their weights are 41, 76, 97, 126 and 166 pounds. Determine the position, blood group, age, height and weight of each of them with the help of the following ten hints. The person on the far right is 37 years older than Jimmy, and is 61 inches tall. Jimmy weighs 56 pounds more than his height. Alexandrio weighs 76 pounds and is 75 inches tall. Justin is type AB and weighs 56 pounds less than Jimmy. The person in the center is 10 years old, is blood type AO and weighs 97 pounds. Andrew, who is the first, is 66 inches tall, and weighs 100 pounds more than his height. The person who is blood type O, is 25 years older than the person to the left of them. Kian is 61 years old. The person who is blood type A, is 55 years younger than Kian and is not next to the person who is type AO. The person who is next to the 10 year old but not next to the person who is 66 inches tall, is blood type B, and weighs 126 pounds.

Six men, namely Martin Freeman, Jonah Jameson, Terry Singer, Mike Cooper, Jim Condon and Sylvian Bogard were in an elevator together. Unexpectedly, the lights went out. When the lights came back, Martin Freeman’s wallet was missing which contained a confidential item. Detectives were called at the scene. They interrogated the suspects, the witnesses, and people who were familiar with the suspects. They collected physical evidence (hair samples, fiber samples, etc.) from the crime scene as well. Overall, they were able to collect fifteen clues, but they could still not find the culprit. Following are the clues. No two suspects have the same weight, color shoes, color umbrella, color car, or hair color. The suspect who owns a pink car was wearing tan shoes. The suspect who weighs 180 pounds owns an orange car. Terry Singer owns an orange car. The suspect who owns a blue car was wearing purple shoes. The suspect who weighs 150 pounds was wearing tan shoes. Mike Cooper was carrying a pink umbrella. Sylvian Bogard has black hair. Jonah Jameson weighs 210 pounds. The suspect who weighs 190 pounds was wearing purple shoes. The suspect who was carrying a black umbrella is not the one who was wearing blue shoes. The thief owns a blue car. The suspect who owns a white car is not the one who weighs 170 pounds. Jim Condon was wearing brown shoes. The suspect who weighs 190 pounds is not the one who has black hair. Can you find the culprit?