The number of story books in the library is 1 / 4 more than that of literature and art books. What is the ratio of literature and art books to story books A 5：9 B 5:4 C 4:5

The number of story books in the library is 1 / 4 more than that of literature and art books. What is the ratio of literature and art books to story books A 5：9 B 5:4 C 4:5

1：（1+1/4）=4:5
Choose C 4:5

Among them, 180 are reference books, 13 are science and technology books, and 15 are literature and art books?

15 + 1 = 16; 180 ^ (1-13-16), = 180 ^ 12, = 360 (copies); a: a total of 360 copies of the three books were purchased

There are three kinds of books in the library, of which 180 are reference books, 3 / 1 are science and technology books, and 5 / 1 are literature and art books. How many books are there in total
I'm only a sixth grade student. This question is from Donghua primary school,

There are three kinds of books in total
180+1/3x+(180+1/3x)/5=x
180+1/3x+36+1/15x=x
216=3/5x
x=360
A: there are 360 books in total

As shown in the figure, in the plane rectangular coordinate system, the parabola y = - x2 + 2x + 3 intersects the X axis at two points a and B, and intersects the Y axis at point C

What is the formula of one cubic meter of C20 concrete?

Water: 175KG, cement: 343kg, sand: 621kg, stone: 1261kg, mix ratio: 0.51:1:1.81:3.6842.5r

The polynomial x2 + 1 plus a monomial makes it a complete square of an integer. Please write two monomials that meet the conditions______ ．

By expanding (x + 1) 2 and (x-1) 2, we get x2 + 2x + 1 and x2-2x + 1. So the conditional monomials are 2x and - 2x

Curve integral of a high number to arc length
∫ L (x ^ 2 + y ^ 2) * Z DS L is an arc corresponding to t from 0 to 1 on the spiral x = tcost, y = TSINT, z = t

The parameter equation gives the trajectory! The integral is to find the mass! First of all, we need to change DS into the form of T! I remember the specific process in the textbook! Tongji version

Is the rate of advance between volume units 1000?

No, the rate of advance between adjacent volume units is 1000

Calculate a ^ - 2BC ^ - 1 ÷ (- B ^ 2C) ^ 3
As soon as possible before tomorrow

The original formula = - A ^ - 2BC ^ - 1 △ B ^ 6C ^ 3
=-a^-2b^(1-6)c^(-1-3)
=-a^-2b^-5c^-4

In the plane rectangular coordinate system xoy, the focus of the parabola y2 = 4x is f, and points a and B are two moving points on the parabola different from point O, and
Vector OA multiplied by OB = 0
Verification: straight line AB passes through fixed point

Let a (x1, Y1) and B (X2, Y2) have: Y1 & # 178; = 4x1, Y2 & # 178; = 4x2. According to the meaning of the problem, let the equation of the straight line AB be x + my = B (B ≠ 0), then there is: x = b-my, substituting Y & # 178; = 4x, we can get: Y & # 178; + 4my-4b = 0; from Weida's theorem, we can get: y1y2 = - 4B, then there is