Introduction to natural numbers Natural numbers refer to numbers used to measure the number of things or to indicate the order of things. Natural numbers start from 0, one by one, forming an infinite group. There are addition and multiplication operations in the set of natural numbers, and the result of adding or multiplying two natural numbers is still a natural number; You can also do subtraction or division, but the result of subtraction and division is not necessarily a natural number, so subtraction and division operations may not be established in the set of natural numbers.
The application of natural numbers is 1, and natural number series is widely used in "series" because in all series, the serial number of each item constitutes a natural number series.
The general term formula of any series can be regarded as a fixed quantitative relationship between the number of each item in the series and its serial number.
2. When calculating how many angles can be formed by n rays, apply the first n terms and formulas of natural sequence.
The 1 ray forms an angle of N- 1 with other rays, and the second ray forms an angle of n-2 with other rays, and so on.
1+2+3+4+……+n- 1 = n(n- 1)/2
3. When finding out how many segments there are n points on a straight line, the first n terms and formulas of natural sequence should also be calculated.
The 1 point and other points form the N- 1 line segment, and the second point and other points form the n-2 line segment, and so on.
1+2+3+4+……+n- 1 = n(n- 1)/2
Example of natural number 1 Xiaoming wrote 1 00 from1. How many figures did he write?
Solution: Classification calculation:
The number of "1" appearing in the cell is:
1, 1 1,2 1,3 1,4 1,5 1,6 1,7 1,8 1,966.
"1" appears in the tenth digit:
10, 1 1, 12, 13, 14, 15, 16, 17, 18,666.
The number of "1" in the hundreds is:100 * * *1;
* * * 10+ 10+ 1 = 2 1.
Example 2 A picture book is *** 100 pages. When typesetting, a font can only arrange one digit. Please calculate how many fonts are used in the page numbers of this book.
Solution: Classification calculation:
From page 1 to page 9, * * 9, each page uses 1 type, * * uses 1×9=9 (pieces);
From page 10 to page 99, * * 90 pages, each page uses 2 kinds, * * uses 2×90= 180 (pieces);
On page 100, only page 1 * * uses three types, so the total number of types used on page * * * of book 100 is:
9+ 180+3= 192 (pieces).
The above is some information about natural numbers for your reference.