2. Counting units refer to: one, ten, one hundred, one thousand, ten thousand, one hundred thousand, one million, ten million, one hundred million, etc.
3. The forward rate between every two adjacent counting units is 10, which is called decimal counting method.
4. Numbers divisible by 2 are called even numbers, 0 is even numbers, and numbers divisible by 2 are called odd numbers.
5, a number, if only 1 and its own two divisors, such a number is called a prime number, such as 2, 3, 5, 7, 1 1, 13 and so on.
If a number has other divisors besides 1 and itself, then it is called a composite number. For example, 4, 6, 8, 9 and 10 are all complex numbers.
6. The minimum natural number is 0, the minimum prime number is 2, and the minimum composite number is 4. Two numbers whose common factor is only 1 are called prime numbers.
7. For the convenience of counting, larger numbers can be rewritten into numbers in tens of thousands or hundreds of millions. The rewritten number is the exact number of the original number. For example, if 1254300000 is rewritten into ten thousand, the number is125430000; Rewritten into a number of 65.438+025.43 billion in units of hundreds of millions.
8. Roundabout: According to actual needs, we can also use a similar number to represent a larger number and omit the mantissa after a certain number. For example: 13024900 15 The mantissa after omitting 100 million is1300 million.
9. Rounding method: If the highest digit of the mantissa to be omitted is 4 or less, the mantissa is removed; If the digit with the highest mantissa is 5 or more, the mantissa is truncated and 1 is added to its previous digit.
10, Law of Quotient Invariance: In division, the dividend and divisor expand or shrink by the same multiple at the same time, and the quotient remains unchanged.
1 1, the nature of the decimal: add or remove zero at the end of the decimal, and the size of the decimal remains unchanged.