Story books are 320 more than science and technology books, three times as many as science and technology books

Story books are 320 more than science and technology books, three times as many as science and technology books

Set: story book as X; science and technology book as y
X-Y=320；X/Y=3
X=3Y,3Y-Y=320
Y=160
X-160=320,X=480

The price of two story books and three science and technology books is 24.3 yuan. The price of three story books and two science and technology books is 23.2 yuan

24.3-23.2 = 1.1 yuan how much more is a science book than a story book
Let the story book be X
3(X+1.1)+2x=2(x+1.1)+3x+1.1
x=4.25
Science and technology book: 4.25 + 1.1 = 5.35
Just do this problem, draw a sword to help

There are 177 science and technology books, story books and literature and art books in the book corner of class 6 and class 3. If there are two more science and technology books and three less story books, and the number of literature and art books is divided by two, then
The number of the three books is the same. How many of them are there?
(to list formulas)

Solution of a series of equations
Suppose there are as many as three kinds of books, all of which have X copies
So there are x - 2 Science and technology books, x + 3 story books and 2x literature and art books
（x-2）+（x+3）+2x=177
2x+1+2x=177
4x+1=177
4x=177-1
4x=176
x=176/4
x=44
Science and technology book: 44-2 = 42
Story book: 44 + 3 = 47
Literature and art books: 44 * 2 = 88
A: there are 42 science and technology books, 47 story books and 88 literature and art books

It costs 20 yuan to buy a story book and a science and technology book, and 72 yuan to buy the same three story books and four science and technology books. How much is a story book? How much is a science and technology book
How much is the book

If the story book costs X Yuan and the science and technology book costs y yuan, there will be:
x+y=20（1）
3x+4y=72（2）
(2) (1) × 3: 4y-3y = 72-60 = 12;
y=12；
Bring in (1) to get: 12 + x = 20;
x=8；
So a story book costs 8 yuan, and a science book costs 12 yuan

A and B are two cylindrical containers with water. The ratio of bottom area is 4:3. The water depth of container a is 7cm, and that of container B is 3cm. Now inject the same amount of water into each container until the water depth is equal (no overflow). How many cm is the water depth?

（7-3）÷（4-3）＝4
A rise 4x3 = 12
B rise 4x4 = 16
The original water depth difference between a and B is 7-3 = 4cm
The increase of water depth after pouring is inversely proportional to the bottom area
——————————————————————————————————————
The increase of water depth after pouring is inversely proportional to the bottom area
Using the solution of the equation, let a rise by x cm, and let B rise by (4 / 3) x for the same amount of water
7+x=3+(4/3)x

It is known that the opposite number of a is 123 and the reciprocal of B is - 212

Because the opposite number of a is 123, then a = - 123, and because the reciprocal of B is - 212, then B = 1 △ (- 212) = - 25. So a + 3ba − 2B = − 123 + 3 × (− 25) − 123 − 2 × (− 25) = (- 53-65) ± (- 53 + 45) = (- 2515 − 1815) × (− 2515 + 1215) = (− 4315) × (− 1315) = 4315 × 1513 = 4313

If a and B are rational numbers, define a new operation △ B = 2ab-1, for example (- 3) △ 4 = 2 × (- 3) × 4-1 = - 25, then [3 △ 2] △ 1=______ ．

According to the new definition in the question: 3 △ (- 2) = 2 × 3 × (- 2) - 1 = - 12-1 = - 13, then [3 △ (- 2)] △ 1 = (- 13) △ 1 = 2 × (- 13) × 1 = - 26-1 = - 27

There are 42 fewer pear trees than apple trees in the orchard. The number of apple trees is three times that of pear trees. How many apple trees and pear trees are there?

Apple 63 pear 21

Given A-B = 3, B + C = - 5, then the value of the algebraic expression AC BC + AA AB is

ac-bc+aa-ab
=(a-b)c+a(a-b)
=3c+3a
=3(c+a)
From A-B = 3, B + C = - 5, we get a + C = - 2
Original formula = 3 * (- 2)
=-6

Each bottle of a brand beverage costs 3 yuan. For those who buy more than three bottles (including three bottles), the supermarket will offer two kinds of preferential treatments: A and B
A: 20% off the original price
B: two bottles at the original price, and the rest at 70% off the original price
(1) If you buy 10 bottles of the brand beverage, which supermarket is the most favorable?
(2) How many bottles can I buy? How many bottles can I buy

(1) A: 3 * 10 * 0.8 = 24 yuan
B: 2 * 3 + 8 * 3 * 0.7 = 6 + 16.8 = 22.8 yuan
(2) When you buy x bottles, the two methods are the same
0.8*3x=2*3+0.7*3x
X = 20 bottles