In the square matrix problem, horizontal lines are called rows and vertical lines are called columns. If the number of rows and columns is equal, it just forms a square, which is called a square. Square matrix is divided into solid square matrix and hollow square matrix.

A solid phalanx means that there is no vacancy in the whole phalanx, and all of them are evenly filled with people or things. A hollow square is a square with a gap in the middle.

Classification of primary schools

Normalization, induction, sum and difference, sum and many, difference and many, meeting, catching up, planting trees, age, sailing, train, clock, profit and loss problem, engineering, positive and negative ratio, proportional distribution, percentage, cattle grazing, chickens and rabbits in the same cage, phalanx, commodity profit.

Deposit interest rate problem, solution concentration problem, composition layout problem, magic square problem, pigeonhole principle problem, agreed multiple problem, maximum problem? .