1 double entry is a common method in lottery betting, and it has a fixed calculation formula. No.3 middle school no.3 middle school. A calculate the product of three numbers starting from 5: 5 * 4 * 3 = 60; (5 digits).

B Calculate the product of three numbers from 1, 3 * 2 *1= 6; The quotient of the two products of 3)C in 3 is the number of groups or notes: 60/6= 10 Note (group) 3. Extension: the calculation method of n in other numbers is the same and can be used universally.

Interpretation of complex numbers.

5 numbers, choose 3, there are 60 combinations.

It is an abstract concept for counting, marking or measuring, and it is a simple symbolic record form (or measurement) of things with the same nature or homogeneity. A series of symbols representing numbers, including numbers and operation symbols, are collectively called the numeration system.

In daily life, numbers usually appear on signs (such as roads, telephone numbers and house numbers), serial indicators (serial numbers) and codes (ISBN). In mathematics, the definition of number is extended to include abstract concepts such as fraction, negative number, irrational number, transcendental number and complex number.