Problems
Michael made a cube with edge \(1\) out of eight bars as on the picture. It is known that all the bars, regardless of color have the same volume, the grey bars are the same and the white bars are also the same. Find the lengths of the edges of the white bar.
One cell was cut out of a rectangle \(3\times 6\). How to glue this cell in another place to get a figure that can be cut into two identical ones? The resulting parts can be rotated and reflected.
In the arithmetic puzzle different letters denote different digits and the same letters denote the same digit. \[P.Z + T.C + D.R + O.B + E.Y\] It turned out that all five terms are not integers, but the sum itself is an integer. Find the sum of the expression. For each possible answer, write one example with these five terms. Explain why other numbers cannot be obtained.
Peter came to the Museum of Modern Art and saw a square painting in a frame of an unusual shape, consisting of \(21\) equal triangles. Peter was interested in what the angles of these triangles were equal to. Help him find them.
Red, blue and green chameleons live on the island, one day \(35\) chameleons stood in a circle. A minute later, they all changed color at the same time, each changed into the color of one of their neighbours. A minute later, everyone again changed the colors at the same time into the color of one of their neighbours. Could it turn out that each chameleon turned red, blue, and green at some point?
A useful common problem-solving strategy is to divide a problem into cases. We can divide the problem into familiar and unfamiliar cases; easy and difficult cases; typical and extreme cases etc. The division is sometimes suggested by the problem, but oftentimes requires a bit of work first.
If you are stuck on a problem or you are not sure where to begin, gathering data by trying out easy or typical cases first might help you with the following (this list is not exhaustive):
Gaining intuition of the problem
Isolating the difficulties
Quantifying progress on the problem
Setting up or completing inductive arguments
Let us take a look at this strategy in action.
The letters \(A\), \(R\), \(S\) and \(T\) represent different digits from \(1\) to \(9\). The same letters correspond to the same digits, while different letters correspond to different digits.
Find \(ART\), given that \(ARTS+STAR=10,T31\).
Split the numbers from \(1\) to \(9\) into three triplets such that the sum of the three numbers in each triplet is prime. For example, if you split them into \(124\), \(356\) and \(789\), then the triplet \(124\) is correct, since \(1+2+4=7\) is prime. But the other two triples are incorrect, since \(3+5+6=14\) and \(7+8+9=24\) are not prime.
A family is going on a big holiday, visiting Austria, Bulgaria, Cyprus, Denmark and Estonia. They want to go to Estonia before Bulgaria. How many ways can they visit the five countries, subject to this constraint?
Let \(p\), \(q\) and \(r\) be distinct primes at least \(5\). Can \(p^2+q^2+r^2\) be prime? If yes, then give an example. If no, then prove it.