Brain games: puzzles, riddles, and logical games.
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Numbers in a square Patterns and correspondences  Weight: 1 Liked the puzzle: 80% 24.12.2011
Place numbers 1,2,.., 9 without repetitions into a 3x3 square so that the sums in all rows, columns, and diagonals are all equal.
Comments:  1 check your solution  
Defective balls Weighing puzzles  Weight: 1 Liked the puzzle: 100% 03.02.2011
A Megamind has ordered a set of steel balls for his scientific experiments: 2 red, 2 orange, 2 yellow, 2 green, and 2 blue. The order was fulfilled but the balls of some color were made 1g lighter than the others. The Megamind has a balance scale that shows the exact weight differential between the two cups. He needs to determine the defective color using one weighing. Please, help the Megamind to do this.
Comments:  1 check your solution  
Two incense sticks Logic puzzles  Weight: 1 Liked the puzzle: 100% 27.12.2009
You have two incense sticks, that burn unevenly, and a lighter. Each will burn for an hour. How can you time 45 minutes using nothing but these tools.
Comments:  4 check your solution  
8 coins Weighing puzzles  Weight: 1 Liked the puzzle: 100% 30.12.2009
You have 8 coins that appear to be identical, except one (which is counterfeit) is slightly heavier than the others. What is the minimal number of weighings on the balance scale that is required to find the counterfeit coin?
Comments:  1 check your solution  
Obtain 24 Algebra, arithmetic  Weight: 2 Liked the puzzle: 100% 27.12.2009
Using numbers 1,3,4,6, and basic arithmetic operations (addition, subtraction, multiplication, and division) and parentheses, obtain and expression that evaluates to 24. You may use only these numbers and only these operations. Every number should be used exactly once. Numbers cannot be concatenated, i.e. you cannot use 13 or 146.
Comments:  7 check your solution  
Milk, lemonade, water, and coke Patterns and correspondences  Weight: 2 Liked the puzzle: 100% 27.01.2011
A bottle,a glass, a carafe, and a can contain milk, lemonade, water, and coke. Water and milk are not in the bottle. The container with lemonade is immediately between the carafe and the container with coke. The can does not contain lemonade or water. The glass is next to the can and the container with milk. The containers form a row. How exactly are they arranged?
Comments:  4 check your solution  
Two villages Knights, Knaves and Jokers  Weight: 2 Liked the puzzle: 100% 27.12.2009
A Megamind is lost in the mountains. He is standing on a path, shouting for help. Finally, he sees a local approaching. Megamind knows that the locals can be knights that always tell the truth, or knaves that always lie. He also knows that the path leads to the village of knights in one direction and to the village of knaves in the other. The problems is that the knaves are also hateful of Megaminds, and will stone him if gets to their village. How can Megamind ask one question and determine the right way to go?
Comments:  4 check your solution  
The fifth number Algebra, arithmetic  Weight: 3 Liked the puzzle: 100% 09.01.2010
The set of numbers 1,3,8,120 has a remarkable property: the product of any two numbers is a perfect square minus one. Find a fifth number that could be added to the set preserving its property.
Comments:  4 check your solution  
50 coins Logic puzzles  Weight: 3 Liked the puzzle: 100% 27.12.2009
Once upon a time, a tsar was holding a reception and the Megamind was among the guests. The tsar decided to test how smart the Megamind was, took him into a dark room, and gave the following task: On the table in this room, there are 50 coins, exactly 10 of them are tails up. In the darkness, it is impossible to determine the sides of these coins. Touching the coins also does not help. The Megamind has to separate these coins into two groups so that the number of tails in both are equal. Can he do it?
Comments:  4 check your solution  
Weights Weighing puzzles  Weight: 3 Liked the puzzle: 100% 29.01.2010
What is the minimal number of weights required to be able to balance all integer weights 1,2,...,40 on a balance scale? Justify the minimality.
Comments:  4 check your solution  
A circle of lies Knights, Knaves and Jokers  Weight: 4 Liked the puzzle: 100% 16.01.2010
After a shipwreck, a MegaMind found himself on an island where some natives always lie and some always tell the truth. As a ritual, all natives stood in a circle facing the center, joined their hands and everybody told the MegaMind whether his right hand side neighbor is a liar or a truth-teller. Based on this information, the MegaMind was able to determine the exact percentage of natives that tell the truth. Can you also determine this percentage?
Comments:  2 check your solution  
The mouse hunt Games puzzles  Weight: 4 Liked the puzzle: 100% 11.01.2010
A smart cat named Leopold is hunting a mouse. A mouse is hiding in one of five holes arranged in a row. Leopold can reach into one of the holes and try to catch the mouse. If he is not successful, the scared mouse runs into a right/left neighboring hole. Is it guaranteed that Leopold will catch the mouse? If so, what should he do?
Comments:  10 check your solution  
Tic-tac-toe, the Megamind style Games puzzles  Weight: 4 Liked the puzzle: 100% 26.02.2011
Two Megaminds decided to play tic-tac-toe using new rules. They use a regular 3x3 playing pad, but each player can choose to place either an X or an O into one of the cells. The winner is still the one who arranges three X's or three O's in a line. Is there a winning strategy in this game? Which player has it?
Comments:  1 check your solution  
18 crystals Weighing puzzles  Weight: 5 Liked the puzzle: 100% 30.12.2009
Once upon a time, a Megamind worked as an optometrist for an Occupier who was color blind. The Occupier had a dream that he may regain perfect vision if the Megamind made him a set of 9 red and 9 blue crystals. The crystals should be of the same size, but the blue ones should be heavier than the red ones. Crystals of the same color should weigh the same. The Megamind completed the order and brought two sets of crystals: blue in his right hand and red in the left. The Occupier was suspicious, he did not trust the Megamind. Fortunately, the Occupier has a balance scale. How can the Megamind convince the Occupier that all crystals in one hand are blue and in the other - red. He can use no more than three weighings.
Comments:  5 check your solution  
The telephone cable 2 Geometry puzzles  Weight: 5 Liked the puzzle: 100% 01.01.2010
The Megamind has a square parcel of land of size 1x1 km. Accidentally, he has found out that the devious Occupants had buried a telephone cable through his land and use it for their devious communications. The cable is buried along a straight line crossing the square land plot. After discovering this, the Megamind got his shovel and... paused to think. What is the shortest trench that the Megamind has to dig to find the cable? The trench may be disconnected. The proof of optimality is not required.
Comments:  3 check your solution  
Ladders with missing steps Logic puzzles  Weight: 5 Liked the puzzle: 100% 17.01.2010
To fix his roof, Megamind needs to climb up a ladder. He has found many ladders to choose from, but unfortunately some of them were missing steps. Megamind cannot climb a ladder if it is missing two or more steps in a row. Originally, all ladders had N steps, marked bottom to top. How many different ladders can Megamind climb?
Comments:  3 check your solution  



 
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