How to convert the quantity, particle number, mass and molar mass of matter

How to convert the quantity, particle number, mass and molar mass of matter

Quantity of substance = mass △ molar mass
Number of particles = amount of matter × Na (Avogadro constant)

The calculation formula between the quantity of matter and the number of particles of matter

Number of particles of matter = quantity of matter x Avogadro constant

What is 1 + 2 + 3 + 4 + 5. + 199 + 200

1+2+3+4+5.+199+200
=（1+200）×200÷2
=20100

How to understand the properties of equivalence relations between matrices?
The equivalence relation between matrices has the following properties
1. Reflexivity
2. Symmetry
3. Transitivity

Reflexivity:
Matrix A and a are equivalent
Symmetry:
If matrix A and B are equivalent, then B and a are also equivalent
Transitivity:
Matrix A and B are equivalent, matrix B and C are equivalent, then a and C are equivalent

2001 times 2003 times (2001 times one in 2002 plus 2002 times one in 2003) (hint: using the law of multiplicative distribution)

2001x2003x(2001/2002-2002/2003)
=2001x2001x2003/2002-2001x2002
=2001x(2001x2003-2002x2002)/2002
=2001x((2002+1)x(2002-1)-2002x2002)/2002
=2001x(2002x2002-1-2002x2002)/2002
=-2001/2002
The result was 2001 out of 2002

It is known that 2 ^ 24-1 can be divided by two numbers between 60 and 70?

2^24-1
=(2^12+1)(2^12-1)
=(2^12+1)(2^6+1)(2^6-1)
=(2^12+1)*65*63
The two numbers are 63 and 65

Adding operational symbols to the four numbers in 289 is equal to 24

8*(2+9-8)=24

Isn't it true that the absolute value is always non negative? Then why do those formulas have | a | = - a,

If | a | = - A,
So a ≤ 0,
If a = - 3, there is | - 3 | = 3,
Then - a = - (- 3) = 3 is nonnegative when a = - 3

There are less than 95 books in the library, including half of science and technology books, one fifth of story books and one ninth of comic books. The rest are joke books. How many are there?

The total number of books in this book corner is a common multiple of 2 and 5 and 9,
The least common multiple of 2,5,9 is 90,
There are no more than 95 books in the known book corner
Therefore, there are 90 books in this book corner
Joke books have = 90 × (1-1 / 2-1 / 5-1 / 9) = 90 × 17 / 90 = 17 (copies)

It is known that the circumference of an isosceles triangle is 120cm, and one side is 30cm?

If 30cm is the bottom edge
The other two waist (120-30) △ 2 = 90 △ 2 = 45cm
If 30 cm is the waist
120-30x2=60cm
30+30=60
So it doesn't match
The other two are 45 cm