1. THE THREE SWITCHES
You are outside a closed room with three light switches. Inside the room is one light bulb. You can turn on and off the switches as much as you like, but you can enter the room only once. How can you determine which switch controls the light bulb?
Turn on the first switch and leave it on for a few minutes, then turn it off and quickly turn on the second switch. Enter the room — if the bulb is lit, it’s the second; if it’s off but warm, it’s the first; if it’s off and cold, it’s the third.
2. THE BROKEN CLOCK
A clock stops every day for exactly 10 minutes, always at the same time. If it was showing the correct time on January 1st at noon, how many days will it take until it shows the correct time again?
72 days. Because the clock loses 10 minutes per day, it will be 12 hours behind after 72 days (12 hours = 720 minutes).
3. THE TRUTH AND LIES
You meet two twins: one always tells the truth, the other always lies. You don’t know who is who. You can ask only one question to one of them to find out which road leads to the city. What do you ask?
Ask, “If I asked your brother which road leads to the city, what would he say?” Then take the opposite road.
4. THE THREE BOXES
One box contains only apples, one only oranges, and one both. All are incorrectly labeled. You can take out only one fruit from one box to check. How can you correct all labels?
Take one fruit from the box labeled “Apples and Oranges”. Whatever you pick, that box contains only that fruit. Then relabel accordingly.
5. THE AGE RIDDLE
A mother is 30 years older than her daughter. In 5 years, the mother will be twice as old as her daughter. How old are they now?
The daughter is 25 years old, the mother is 55.
1. Define:
Let the daughter’s current age be x years.
Then the mother’s current age is x + 30 years.
2. In 5 years:
The daughter will be x + 5,
The mother will be x + 30 + 5 = x + 35.
3. Condition:
In 5 years, the mother will be twice as old as the daughter:
x + 35 = 2(x + 5)
4. Solve the equation:
x + 35 = 2x + 10
35 − 10 = 2x − x
x = 25
Therefore:
The daughter is 25 years old,
The mother is 25 + 30 = 55 years old.
6. THE CHESSBOARD PUZZLE
A standard chessboard has 64 squares. Two opposite corners are removed. Can you cover the remaining board completely with 31 dominoes, each covering two squares?
No. Removing two opposite corners leaves unequal numbers of black and white squares, while each domino must cover one of each.
7. THE COIN WEIGHT
You have 8 coins, all identical except one that is slightly heavier. Using a balance scale, what is the minimum number of weighings needed to find the heavier coin?
2 weighings. First, weigh 3 vs 3. Depending on which side is heavier, take those 3 and weigh 1 vs 1.
8. THE CALENDAR QUESTION
Two people were born in the same year, month, and day, yet their birthdays are always on different days of the week. How is this possible?
They were born in different time zones, on opposite sides of the world.
9. THE RIVER CROSSING
A farmer needs to cross a river with a wolf, a goat, and a cabbage. He can take only one at a time. If left alone, the wolf eats the goat, and the goat eats the cabbage. How can he get all across safely?
Take the goat first. Return alone, take the wolf, bring back the goat, take the cabbage, return alone, and finally take the goat again.
10. EINSTEIN’S LOGIC PUZZLE
There are five houses in a row.
Each house has a different color, and in each lives a person of a different nationality.
Each person drinks a different beverage, smokes a different brand of cigarettes, and keeps a different pet.
No two people share the same drink, cigarette brand, or pet.
Find out: Who owns the fish?
Clues:
1. The Brit lives in the red house.
2. The Swede keeps dogs.
3. The Dane drinks tea.
4. The green house is immediately to the left of the white house.
5. The owner of the green house drinks coffee.
6. The person who smokes “Pall Mall” keeps birds.
7. The owner of the yellow house smokes “Dunhill.”
8. The resident of the middle (third) house drinks milk.
9. The Norwegian lives in the first house.
10. The “Blends” smoker lives next to the person who has cats.
11. The person who keeps horses lives next to the “Dunhill” smoker.
12. The “BlueMaster” smoker drinks beer.
13. The German smokes “Prince.”
14. The Norwegian lives next to the blue house.
15. The “Blends” smoker has a neighbor who drinks water.
The German owns the fish.
