Significant number of approximate number If the repeated number is a significant number, such as 0.01223, is the significant number three 123s or four 1223, or 0.00125004, is the significant number five 12504, or six 125004, or 0.102405, is the significant number five 10245, or six 102405, please answer

Significant number of approximate number If the repeated number is a significant number, such as 0.01223, is the significant number three 123s or four 1223, or 0.00125004, is the significant number five 12504, or six 125004, or 0.102405, is the significant number five 10245, or six 102405, please answer

Yes, for example, 0.01223, the significant number is 1223

Approximate number significant number
259950 (accurate to hundreds) 2.33 * 10 ^ 3 keep a few significant digits 2.020 * 10 ^ 3 keep a few significant digits?
If you don't understand 10 ^ 3, you can see it as the third power of 10

2.600* 10^5
Three
Four

On the problem of significant number and approximate number
1: The third power of 1.0 * 10
1 billion 354 million 320 thousand
two thousand three hundred and nine
Which one are they accurate to? How many significant numbers are there?
In addition, please tell me the law about this kind of problem

The third power of 1.0 * 10 is accurate to 100 digits, with two significant digits
135432 million, accurate to 10000, 6 significant figures
2309 to the nearest digit, 4 significant digits
The significant number starts from the first digit which is not 0 and ends at the last digit (including the following 0), such as 0.001230000. The significant number starts from the first "1" which is not 0. There are 7 digits (including the last 4 zeros) and 7 significant digits
In addition, for those with the power of 10, the significant digits only count to the front part, such as 1.0012 * 10 ^ 3, and the significant digits only look at 1.0012, with a total of 5 significant digits, which are accurate to the tenth (the exact number depends on the last digit, the first one in 1.0012 * 10 ^ 3 is thousand, and the last two should be on the tenth)
For 135432 million of such numbers, the significant number is still only the first 135432, with a total of 6 digits. The unit should be included in the exact number, and the last 2 digits above 10000 digits should be accurate to 10000 digits.)

If set a represents a set of natural numbers less than 2, then the elements in set a can be?

The elements in set a can be 0 or 1

From natural numbers 1 to 10, if the absolute value of the difference between any two numbers is taken as the element of set a, then the nonempty proper subsets of set a are common_ individual

A = {1,2,3,4,5,6,7,8,9}, there are 2 ^ 9-2 non empty proper subsets of a = 510

Given the set a = {natural number less than 6}, B = {prime number less than 10} C = {positive factor of 24 and 36, let the number of elements of ABC be ABC respectively
The value of a + B + C is

A=6
B=4
C=6
So a + B + C = 16

How to compare the "number" of infinite set elements -- is rational number "more" than natural number?

Qian Ling (Department of mathematics, Beijing Normal University, 100875) is familiar with the idea of one correspondence, which can be found everywhere in mathematics. The purpose of this paper is to introduce the concept of equivalence of two sets by using the method of one correspondence

Why do natural numbers and rational numbers correspond one by one?
I have also seen several methods. Some say that all rational numbers are written in the form of fractions into a table with n rows and N columns, and their serial numbers are the whole set of natural numbers, which corresponds one by one. I also understand that they are alef0
But I think that the rational number itself contains a set of natural numbers, so that the set of natural numbers corresponds to itself one by one, and the rest of the rational number set does not have any natural numbers corresponding to them?

When we say that natural numbers and rational numbers can be one-to-one corresponding, we mean that we can find a corresponding rule. Under this corresponding rule, two sets can be one-to-one corresponding. It doesn't mean that "any correspondence" between the two sets is one-to-one corresponding. According to your opinion, natural numbers and natural numbers can't be one-to-one corresponding, for example, the one on the left

Constructing a one-to-one correspondence between all rational number sets and all natural number sets

N=|[x]|
[x] Represents an integer not greater than x, which belongs to the set of all rational numbers

Why are there as many natural numbers as rational numbers?
Tip: Here's an analysis of a person I saw:
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Rational numbers can be arranged in a certain order as follows
0,1/2,1/3,2/3,1/4,2/4,3/4,1/5,2/5,3/5,……
Remove the duplicate, such as 2 / 4 (because 2 / 4 = 1 / 2)
In this way, all rational numbers are arranged into a series of numbers in a certain order, so rational numbers and natural numbers are one-to-one corresponding, so rational numbers are as many as natural numbers, they are countable sets, and the cardinality is the same
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But I can't understand it. Who can make it clear? Thank you very much!
But this is the subject of independent enrollment of Tsinghua University and Peking University.
Proof: there are as many natural numbers as rational numbers

Here is my own way: take any rational number A1, which can be expressed as M1 / N1, that is, A1 corresponds to M1; then take any rational number A2 which is different from the above, which can be expressed as m2 / N2, then M2 is not equal to M1, otherwise, there must be a natural number K2, A2 = k2m2 / k2n2, k2m2 is not equal to M1, then A2 corresponds to the natural number k2m2