Write and read from the upper left corner. Take 25 as an example. When reading, there are two tens in ten places, which are read as 20, and five ones in each place, which are read as 5, and together they are read as 25; When writing numbers, 20 means two tens out of ten, two out of ten, five means five ones in a number, and five in a number, which adds up to 25.

Summary of mathematics knowledge points from grade one to grade six in primary school;

The first grade of primary school: 99 multiplication formula, learn basic addition and subtraction multiplication formula: recite 99 multiplication formula well and be familiar with single-digit multiplication formula;

The second grade of primary school: improve the multiplication formula table, strengthen the knowledge of the first grade, and learn the mixed operation of division and basic geometry;

The third grade of primary school: learn multiplication and commutation law, geometric area perimeter, time and unit. Distance calculation, distribution law, fractional decimal;

The fourth grade of primary school: the natural number of line angle is an integer, the prime factor is trapezoidal symmetry, and the fraction is calculated;

The fifth grade of primary school: multiplication and division of fractions and decimals, algebraic equations and average values, comparative size transformation, graphic area and volume;

Sixth grade: proportional percentage probability, circular fan, cylinder and cone.