In the library, textbooks account for one tenth of the total; literature and art books account for four seventh of the total; science and technology books account for 348; compared with literature and art books In a library, textbooks account for one tenth of the total number, literature and art books account for four seventh of the total number, 348 science and technology books, 12 less than nine fifths of literature and art books. How many textbooks do the library have?

Let the total number be X
So: ((9 / 50) * (4x / 7)) - 348 = 12
x=3500
So the number of textbooks is: (1 / 10) x = 0.1 * 3500 = 350 (copies)
A: there are 350 textbooks in this library

There are 144 science and technology books, one fifth more than literature and art books

X*1.2=144
X=144/1.2
X=120

There are 75 science and technology books in the book corner of class 63. The number of literature and art books is 15 less than that of science and technology books?

20%
There are 75 science and technology books, 15 less literature and art books than science and technology books, less 15 / 75 = 20%

52.6 △ x + 13 = 39.3 find x

How to calculate 98 * 35 simply

98x35
=(100-2)x35
=100x35-2x35
=3500-70
=3430

As shown in the figure, PA is the secant of the circle O, passing through the center O, intersecting the circle O at points a, B, PD, tangent a chord of the circle O, and PC = PD
(1) Verification: PC is the tangent of circle o
(2) If AC = PD, BP = OA

First, draw a graph. (1) prove: because od = OC, PD = PC, PA = PA, so △ PDO ≌ △ PCO, so ∠ PCO = ∠ PDO = 90 °, so PC is the tangent of circle o
(2) It is proved that because PD = PC and AC = PD, PC = AC, so △ PCA is an isosceles triangle, so ∠ cap = ∠ CPA,
In △ PCA, CPA + cap + OCA + PCO = 180 ° because PCO = 90 ° so CPA = 30 ° Po = 2CO, that is, point B is the midpoint of Po, so BP = OA

In order to keep the total amount of sales unchanged, how much more will the sales volume increase than the original price?
Need to explain, why
Is the formula current price * original sales volume = original price?

Equivalence relation: the original price sales is equal to the total amount of promotion. The total amount of original price sales = original price * sales volume (number of pieces) the total amount of promotion sales = promotion price * sales volume (number of pieces). If the original price is taken as 1, the promotion price = 1 * (1-20%). If the original price sales volume is taken as 1, the promotion price sales volume is 1 * (1 + x)

If the square of two-thirds a times the m power of B and the n power of negative zero point five times a times the fourth power of B, then what is m equal to and what is n equal to

If the square of two-thirds a times the m power of B and the n power of negative zero point five times a times the fourth power of B, then what is m equal to and what is n equal to
m=4
n=2

Given that A.B.C is a positive number, we prove that a ^ 2 * B ^ 2 * C ^ 2 > = a ^ (B + C) * B ^ (a + C) * C ^ (a + b)
Many people have misunderstood the topic, I use words to describe it again: only A.B.C is a positive number, to prove: the 2A power of a multiplied by the 2B power of B, the 2C power of C is greater than or equal to the B + C power of a, the a + C power of B, and the a + B power of C

You follow my instructions. It's easy to multiply the left and right sides by two
Turn the one on the right to the left
You can simplify it to (a-b) ^ 2 + (A-C) ^ 2 + (B-C) ^ 2 > = 0

For a commodity, the original price is 300 yuan. First raise the price by one tenth, then lower the price by one tenth

It's 300 × (1 + 1 / 10) × (1-1 / 10) = 297 yuan