Informal "real-world" mathematical problems are questions related to a concrete setting, such as "Adam has five apples and gives John three. How many has he left?". Such questions are usually more difficult to solve than regular mathematical exercises like "5 − 3", even if one knows the mathematics required to solve the problem. Known as word problems, they are used in mathematics education to teach students to connect real-world situations to the abstract language of mathematics. In general, to use mathematics for solving a real-world problem, the first step is to construct a mathematical model of the problem. This involves abstraction from the details of the problem, and the modeller has to be careful not to lose essential aspects in translating the original problem into a mathematical one. After the problem has been solved in the world of mathematics, the solution must be translated back into the context of the original problem. By outward seeing, there is various phenomenon from simple to complex in the real world. The some of that have also the complex mechanism with microscopic observation whereas they have the simple outward look. It depend to the scale of the observation and the of the mechanism. There is not only the case that simple phenomenon explained by the simple model, but also the case that simple model might be able to explain the complex phenomenon. One of example model is a model by the chaos theory.
Abstract problems
Abstract mathematical problems arise in all fields of mathematics. While mathematicians usually study them for their own sake, by doing so results may be obtained that find application outside the realm of mathematics. Theoretical physics has historically been, and remains, a rich source of inspiration. Some abstract problems have been rigorously proved to be unsolvable, such as squaring the circle and trisecting the angle using only the compass and straightedge constructions of classical geometry, and solving the general quintic equation algebraically. Also provably unsolvable are so-called undecidable problems, such as the halting problem for Turing machines. Many abstract problems can be solved routinely, others have been solved with great effort, for some significant inroads have been made without having led yet to a full solution, and yet others have withstood all attempts, such as Goldbach's conjecture and the Collatz conjecture. Some well-known difficult abstract problems that have been solved relatively recently are the four-colour theorem, Fermat's Last Theorem, and the Poincaré conjecture. The all of mathematical new ideas which develop a new horizon on our imagination not correspond to the real world. Science is a way of seeking only new mathematics, if all of that correspond. On the view of modern mathematics, It have thought that to solve a mathematical problem be able to reduced formally to an operation of symbol that restricted by the certain rules like chess. On this meaning, Wittgenstein interpret the mathematics to a language game. So a mathematical problem that not relation to real problem is proposed or attempted to solve by mathematician. And it may be that interest of studying mathematics for the mathematician himself made much than newness or difference on the value judgment of the mathematical work, if mathematics is a game. Popper criticize such viewpoint that is able to accepted in the mathematics but not in other science subjects. Computers do not need to have a sense of the motivations of mathematicians in order to do what they do. Formal definitions and computer-checkable deductions are absolutely central to mathematical science. The vitality of computer-checkable, symbol-based methodologies is not inherent to the rules alone, but rather depends on our imagination.
Degradation of problems to exercises
Mathematics educators using problem solving for evaluation have an issue phrased by Alan H. Schoenfeld: The same issue was faced by Sylvestre Lacroix almost two centuries earlier: Such degradation of problems into exercises is characteristic of mathematics in history. For example, describing the preparations for the Cambridge Mathematical Tripos in the 19th century, Andrew Warwick wrote:
