There are 3200 popular science books in the school library, accounting for two fifths of all books. The number of story books is 25% less than popular science books How many story books are there in the library?

There are 3200 popular science books in the school library, accounting for two fifths of all books. The number of story books is 25% less than popular science books How many story books are there in the library?

There are 2400 story books
1. Column equation: (popular science books - story books) / popular science books = 25%. (divide those who compare)
2. Transformation equation: popular science books story books = 25% popular science books
3. It can be concluded that story books = (1-25%) popular science books = 75% * 3200 = 2400

There are 300 storybooks in the school library. Science and technology books are five thirds of storybooks, and comic books are two fifths of storybooks. How many of the three kinds of books are there altogether?

Science and technology book 300 * 5 / 3 = 500
Comic 300 * 2 / 5 = 120
300+500+120=920
A total of 920 copies

There are 150 story books in the school library, four fifths less than the comic books, 10 less. How many comic books are there?

Hello
(150 + 10) △ 4 / 5
=160 △ 4 / 5
=200 copies
A: there are 200 comic books

1.5 divided by 1.25

1.5/1.25
=(1.5x8)/(1.25x8)
=12/10
=1.2

It is known whether the circle C: x ^ 2 + y ^ 2-2x + 4y-4 = 0 and the straight line L: y = x + B have a straight line L, so that the circle with ab as the diameter crosses the origin when l intersects the circle C at two points A.B

Let there be a straight line L: y = x + B, and substitute it into x ^ 2 + y ^ 2-2x + 4y-4 = 0 to get 2x ^ + 2 (B + 1) x + B ^ + 4b-4 = 0, a (x1, Y1), B (X2, Y2), then X1 + x2 = - (B + 1) ①, x1x2=(b^+4b-4)/2… ② The equation of the circle with the diameter of string AB is: (x-x1) (x-x2) + (Y-Y1) (Y-Y2) = 0, it passes through the origin, ■ (0-x1) (0-x2) + (0-y1) (0-y2) = 0, that is, x1x2 + y1y2 = 0, and y1y2 = (x1 + b) (x2 + b), ｜ 2x1x2 + B (x1 + x2) + B ^ 2 = 0, substituting ① and ② into B ^ 2 + 3b-4 = 0, ｜ B = 1 or B = - 4, the equation of the line L is: y = x + 1 or y = x-4

The solution of the equation is 5x-4-4 X-1 = 1-12 x + 1

3 / 5x-4 / 4 X-1 = 1-12 / x + 1 multiplied by 12
4（5x-4）-3(x-1)=12-(x+1)
20x-16-3x+3=12-x-1
17x-13=11-x
17x+x=11+13
18x=24
x=4/3
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Known set a = {(x, y) / ABS (x) + ABS (y)

Simple calculation of 7 / 8 × 5 / 6 + 1 / 8 △ 6 / 5?

7/8×5/6+1/8÷6/5
=7/8×5/6+1/8×5/6
=(7/8+1/8)×5/6
= 5/6
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There are at least two sets of values of Mn for 1 / M + 1 / N = 1 / 8

I default to m, n is a positive integer to do, otherwise too boring
m=9,n=72
m=16,n=16
Because m and N must be small and large, let m ≤ n
Then: 1 / m ≥ 1 / n
∴1/m+1/n≤1/m+1/m=2/m
∴2/m≥1/8
∴1/m≥1/16
∴m≤16
∴m=9,10,11,12,13,14,15,16.
You can find all possible positive integers by substituting all the numbers above
m=9,n=72
m=10,n=40
M = 11, n = 88 / 3 (rounding off)
m=12,n=24
M = 13, n = 104 / 5 (rounding off)
M = 14, n = 56 / 3 (rounding off)
M = 15, n = 120 / 7 (rounding off)
m=16,n=16
The above can be used to all positive integers (m, n)
（9,72）（10,40）（12,24）（16,16）（24,12）（40,10）（72,9）
If only m and N are integers, we need to substitute M = 1,2,3,4,5,6,7 for negative integers
（m,n）
（4,-8）（6,-24）（-24,6）（-8,4）

Three fourths of the time is equal to a few minutes, seven tenths of a ton is equal to thousands of grams, and two fifths of a meter is equal to a few decimeters,

45 minutes, 700 kg, 4 decimeters