The price of 8 Chinese books and 10 math books is equal. Chinese books cost 40 cents more than math books. How much is each Chinese book?

The price of 8 Chinese books and 10 math books is equal. Chinese books cost 40 cents more than math books. How much is each Chinese book?

If each Chinese book costs X Yuan, the math book costs x-0.4 yuan
Lie equation: 8x = 10 (x-0.4)
The solution is: x = 2
A: 2 yuan per Chinese book

Mr. Hai took 300 yuan to buy a book, and recovered 15 yuan in total, 12 yuan for a Chinese book and 11 yuan for a math book. How many Chinese books and math books did Mr. Hai buy?
Mr. Hai took 300 yuan to buy books, recovered 15 yuan in total, and bought 24 books. It is known that a Chinese book costs 12 yuan and a math book costs 11 yuan. How many Chinese books and math books do Mr. Hai buy?

X Chinese books
12x+11(24-x)+15=300
x=21
24-21=3
There are 21 Chinese books and 3 mathematics books

I need two math books. Chinese and English exchange

I need two math books.

English translation
Teachers told us we could hand in our home the next day?

Sounds right!

Ingenious calculation: 1 of 8 * 9 + 1 of 9 * 10 + 1 of 10 * 11 +... + 1 of 99 * 100=
Please help me! It's a difficult paper! It needs to be clear and easy to understand,

Split each formula, for example: 1 / (8 * 9) = 1 / 8 - 1 / 9
The original formula = (1 / 8) - (1 / 9) + (1 / 9) - (1 / 10) + (1 / 10) - (1 / 11) +. + (1 / 99) - (1 / 100)
=(1/8)-(1/100)
=23/200

If the point a (- m, 1-2m) is symmetrical about the origin in the first quadrant, then the value range of M is in the first quadrant

∵ point a (- m, 1-2m) is symmetric about the origin ∵ (m, - 1 + 2m) ∵ draw the number axis in the first quadrant ∵ m > 0 -- 1 + 2m > 0, 2m > 1 m > 1 / 2

19 + 9 + 1 / 2 + 7 + 1 / 4 + 3 + 1 / 8 + 8 + 1 / 16 + 4 + 1 / 32
Calculate the sum of all three natural numbers
Two passenger and freight cars leave from a and B at the same time. They meet in 4.5 hours. When they meet, the passenger car travels 27 kilometers more than the freight car. The speed of the freight car is four fifths of that of the passenger car. How many kilometers are there between a and B

Solution;
1. The original formula is 19 + 9 + 1 / 2 + 7 + 1 / 4 + 3 + 1 / 8 + 8 + 1 / 16 + 4 + 1 / 32
=(19 + 9 + 7 + 3 + 8 + 4) + (1 / 2 + 1 / 4 + 1 / 8 + 1 / 16 + 1 / 32)
=50 + (1 / 2 + 1 / 4 + 1 / 8 + 1 / 16 + 1 / 32 + 1 / 32-1 / 32)
=50 + (1 / 2 + 1 / 4 + 1 / 8 + 1 / 16 + 1 / 16-1 / 32)
=50 + (1 / 2 + 1 / 4 + 1 / 8 + 1 / 8-1 / 32)
=50 + (1 / 2 + 1 / 4 + 1 / 4-1 / 32)
=50 + (1 / 2 + 1 / 2-1 / 32)
=50 + (1-1 / 32)
=51-1 / 32
=50 and 31 / 32
2、100+101+102+.+998+999
=(100+999)×900÷2
=494550
3. Let the bus speed be x km / h
5 × 5 / 4x + 27 = 4.5X
3.6x+27=4.5x
0.9x=27
x=30
Therefore, the distance between a and B is 30 × 4.5 × 2-27 = 243 km
A: A and B are 243 kilometers apart
Hope to adopt, thank you!

Given that the quadratic function f (x) has two different zeros, x1.x2, and f (2 + x) = f (2-x) holds for any x, then X1 + x2=

F (2 + x) = f (2-x) means that the axis of symmetry is x = 2
So the midpoint of the two is on the axis of symmetry
That is: (x1 + x2) / 2 = 2
x1+x2=4

On the front and back of the three cards, 1 and 2, 4 and 5, 7 and 8 are written respectively. Arrange them into three digits. How many different three digits are there?
We should have a detailed thought of the conclusion

This is a permutation problem. The problem is divided into four steps: 1. Choose one side for the first card; 2. Choose one side for the second card; 3. Choose one side for the third card; 4. Arrange three cards

How to find the n-th derivative of 1 / x power of E?

First find the first order, second order, third order, and then find the law