(1) Interesting "0"

"Level 0" can mean no, "0" can participate in the calculation, "0" acts as a placeholder in the number, and "0" can mean the starting point, indicating 0 degrees.

(2) Cardinality and ordinal number

When expressing the number of objects, use the cardinal number; Ordinal numbers are used to indicate the order in which objects are arranged.

Cardinality is different from ordinal number. Cardinality represents the number of objects, and ordinal number represents the arrangement order of objects.

Second, count.

(A) the number of simple graphics

When counting the number of randomly placed objects or a certain type of graphics, all objects should be marked with serial numbers first, and the designated graphics can be observed and counted according to the serial numbers. Note that for the same object, the observation results will be different from different angles. Therefore, when counting simple figures, we should be good at observing and analyzing problems from different angles.