The school library bought 260 new books, of which 55% are science and technology books, 25% are literature and art books, and the rest are story books. How many are story books?

The school library bought 260 new books, of which 55% are science and technology books, 25% are literature and art books, and the rest are story books. How many are story books?

260 × (1-55% - 25%) = 260 × 20% = 260 × 0.2 = 52 (copies); answer: there are 52 story books

Chunlei primary school library has a total of 40000 books. The distribution of all kinds of books accounts for one third of science and technology, and five of literature and art

One third is four twelfth
Four out of twelve plus five out of twelve = nine out of twelve = three out of four
40000 × (1-3 / 4) = 10000 volumes
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Reading report of five thousand years of China

The witness of history -- reading the five thousand years of China, I feel that the universe is boundless. In the past years, our world has experienced the baptism of many storms and vicissitudes. In the land where we stand, our life is very little for it

How to choose the free variables in the basic solution system of linear algebra?

First, mark the first non-zero number in each row, and remove the columns of the marked numbers, and other columns are the free variables

(1) 2x-3 = 5x-x (2) 3 (x-1) = (x + 2)
(1) 2x-3 = 5x-x (2) 3 (x-1) = (x + 2) transforms the quadratic equation with one variable into a general form

1. 3x－5x－3＝0
2. 2x－5＝0

Given a = {y | y = x & # 178; + 1, X & # 8714; R}, complete set u = R, find the intersection n of CUA

A:y=x²+1≥1;
∴CuA={x|x＜1}
∴CuA∩N={0};
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63 = 18N + 1 / 2 (n-1) n * (- 3), how can n be solved

The original equation can be reduced to: 63 = 18n-3 / 2 * n * (n-1)
Multiply both sides by 2 / 3:42 = 12n-n * (n-1)
The result is: n ^ 2-13n + 42 = 0
The factorization is: (n-6) * (N-7) = 0
So: n = 6 or n = 7

The function f (x) = x / 1 + x ^ 2 is an odd function defined in (- 1,1) and f (1 / 2) = 2 / 5, which solves the inequality f (t-1) + F (T) < 0
And f (x) is an increasing function on (- 1,1)

1. F (x) = (AX + b) / (1 + x ^ 2) because: F (x) is an odd function, so: F (0) = b = 0, that is: F (x) = ax / (1 + x ^ 2). And because f (1 / 2) = 2 / 5, so: a (1 / 2) / (1 + (1 / 2) ^ 2) = 2 / 5, that is: a (1 / 2) / (1 + 1 / 4) = a (2 / 5) = 2 / 5, so: a = 1. Therefore, the analytic formula is: F (x) = x / (1 + x ^ 2). 2

Given that the vertex of a triangle is a (8,5) B (4, - 2) C (- 6,3), the equation of three straight lines passing through the midpoint of each two points is obtained

Three straight lines passing through the midpoint of every two points? Is that the question?
AB midpoint (6,1.5)
BC midpoint (- 1,0.5)
AC midpoint (1,4)
Then the two-point formula is used

A household electric energy meter is marked with "220V 5A 3000r / kW · H". When all the household appliances are working, the electric energy meter turns 12 times in one minute,
It is estimated that the total power of all electrical appliances in the house is________ W. The maximum power that the home can connect is_____ W

W=12r/(3000r/kw·h)=1/250kwh
t=1min=1/60h
Total power of all electrical appliances P = w / T = (1 / 250kwh) / (1 / 60H) = 0.24kw = 240W
Maximum power P = UI = 220 * 5A = 1100W