FEATURED
Schoolyard
Draw 2 squares in the schoolyard in order to separate all students from each other.
SOLUTION
The solution is shown below.
Category: Brain Teasers
A collection of Math, Chess, Detective, Lateral, Insight, Science, Practical, and Deduction puzzles, carefully curated by Puzzle Prime.
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The Frozen Lake
You wake up on a frozen lake in an isolated region, a hundred meters away from the shore. The surface of the lake is frictionless, and no grip of any kind can be attained over it. You find just your mobile phone in your pocket, but when you take it out to call for help, you realize there is no reception.
If there is no wind force to help you escape, what are you going to do to avoid freezing to death?
SOLUTION
Throw your phone as hard as you can. Thanks to Newton’s third law of motion and the frictionless lake, you will start sliding away.
I Had 6 Eggs
I had 6 eggs. Broke two, cooked two, ate two. How many do I have left?
SOLUTION
I have 4 eggs left. I had an omelet with the first 2; that’s why I broke them, cooked them, and ate them.
Mini Chess
White to play and force the black king to d3.
SOLUTION
1. Qc3+ Ka2 2. Qc1 Kb3 3. Qa1 Kc2 4. Qa2+ Kc3 5. Qb1 Kd2 6. Qb2+ Kd1 7. Qa2 Kc1 8. Qb3 Kd2 9. Qb1 Kc3 10. Qa2 Kd3
If 4. … Kc1, then 5. Qb3 and we get to the position in move 8. If 4. … Kd1, then 5. Qb1 Kd2 6. Qb2+ and we get to the position in move 6.
The Missing Word
What single word can be used to complete all the words below:
D E _ _ _ ST
C _ _ _ E R
S T _ _ _
P _ _ _ N T
SOLUTION
The word is ARE.
On Fire
Slylock Fox and Max Mouse needed the rope on the ground to escape, but none of the onlookers could throw it as high as their window. However, Slylock and his sidekick found a solution and managed to escape the fire. What did they do?
SOLUTION
Slylock asked the fisherman to cast his line to their window. After the fishing line was in Slylock’s hands, he told the beaver to remove the remaining line from the reel and tie it to the end of the rope. Slylock used the line to pull the rope up and then went down along it.
FEATURED
10 Dots, 10 Coins
If you have 10 dots on the ground, can you always cover them with 10 pennies without the coins overlapping?
SOLUTION
Assume the dots lie in a plane and the radius of a penny is 1. Make an infinite grid of circles with radii 1, as shown on the picture, and place it randomly in the plane.
If we choose any point in the plane, the probability that it will end up inside some circle of the grid is equal to S(C)/S(H), where S(C) is the area of a coin and S(H) is the area of a regular hexagon circumscribed around it.
FEATURED
Married Couples
In a small village, there are 100 married couples living. Everyone in the village lives by the following two rules:
- If a husband cheats on his wife, and she figures it out, the husband gets killed on the very same day.
- The wives gossip about all the infidelities in town, with the only exception that no woman is told whether her husband has cheated on her.
One day a traveler comes to the village and finds out that every man has cheated at least once on his wife. When he leaves, without being specific, he announces in front of everybody that at least one infidelity has occurred. What will happen in the next 100 days in the village?
SOLUTION
Let us first see what will happen if there are N married couples in the village and K husbands have cheated, where K=1 or 2.
If K = 1, then on the first day the cheating husband would get killed and nobody else will die. If K = 2, then on the first day nobody will get killed. During the second day, however, both women would think like this: “If my husband didn’t cheat on me, then the other woman would have immediately realized that she was being cheated on and would have killed her husband on the first day. This did not happen and therefore my husband has cheated on me.” Then both men will get killed on the second day.
Now assume that if there are N couples on the island and K husbands have cheated, then all K cheaters will get killed on day K. Let us examine what will happen if there are N + 1 couples on the island and L husbands have cheated.
Every woman would think like this: “If I assume that my husband didn’t cheat on me, then the behavior of the remaining N couples will not be influenced by my family’s presence on the island.” Therefore, she has to wait and see when and how many men will get killed in the village. After L days pass however and nobody gets killed, every woman who has been cheated on will realize that her assumption is wrong and will kill her husband on the next day. Therefore, if there are N + 1 couples on the island, again all L cheating husbands will get killed on day L.
Applying this inductive logic consecutively for 3 couples, 4 couples, 5 couples, etc., we see that when there are 100 married couples on the island, all men will get killed on day 100.
The Father
Warning: this puzzle involves mature themes that are inappropriate for younger audiences. If you are not an adult, please skip this puzzle.
SHOW PUZZLE
Mary is 21 years older than her son. After 6 years, she will be 5 times older than him. Where is the father?
SOLUTION
Let M be the age of the mother and S be the age of the son. We have M = S + 21 and M + 6 = 5(S + 6). We solve the system and get S= -3/4, i.e. minus 9 months. Therefore right now the son just got conceived and the father is with the mother.
Division Impossible
Can you divide the following shape into 4 identical pieces?
Remark: The pattern is not important.
SOLUTION
Divide the piece into 4 smaller pieces that have the same shape and half dimensions.
