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Bacterium Algebra, arithmetic  Weight: 1 Liked the puzzle: 91% 26.12.2009
A certain type of bacteria double every second. If we put one bacterium in a Petri dish, the dish will fill in 1 minute. How long will it take to fill the dish, if we start with 2 bacteria?
Comments:  3 | check your solution  
Defective pixel Algebra, arithmetic  Weight: 1 Liked the puzzle: 100% 03.01.2010

There is true expression on panel. But only one pixel is defective. Which one?

Press for see in full size.
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  
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  
The 40th anniversary tournament Algebra, arithmetic  Weight: 5 Liked the puzzle: 100% 05.01.2010
Once upon a time, grandfather Megamind told his grandchildren the following tale: On the 40th anniversary of their town, a soccer tournament was held in the central park. Five teams played with each other, 3 points were given for a win, and 1 point was given for tie. Each team earned a different number of points. The goal total was 40. But most curiously, a team placed higher scored fewer and gave up more goals than a team placed lower. Could such tournament really have taken place or is it possible that the old Megamind finally felt his age?
Comments:  1 | check your solution  
10101...01 Algebra, arithmetic  Weight: 5 Liked the puzzle: 100% 07.02.2010
For which values of n, the decimal number 10101..01 (the alternating sequence of n ones and n-1 zeros) is a prime?
Comments:  1 | check your solution  
Rabbits in the store Algebra, arithmetic  Weight: 5 Liked the puzzle: 100% 09.02.2011
In a pet store, the first Megamind bought two plus a half of the remaining rabbits. The second Megamind bought three plus a third of the remaining rabbits. The third Megamind bought four plus a fourth of the remaining rabbits. At some point, one of the Megaminds could not make his purchase. What is the maximal number of satisfied customers (Megaminds)?
Comments:  3 | check your solution  
The players' weights Algebra, arithmetic  Weight: 5 Liked the puzzle: 04.03.2011
Once upon a time, 23 Megaminds decided to play a soccer game. In the process of choosing teams, they observed a curious property: no matter who was elected as a referee, the remaining 22 players could be split into two teams with equal total weight. Is it possible that not all Megaminds weighed equally? Each Megamind weighed an integer number of kilograms.
Comments:  1 | check your solution  
Sum of all divisors of a square Algebra, arithmetic  Weight: 5 Liked the puzzle: 50% 19.03.2011
Prove that the sum of all divisors of a nonzero square integer is odd.
Comments:  1 | check your solution  



 
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