The school library originally had 3600 books, 30% of which were comic books, and the rest were science and technology books. Later, it bought a batch of comic books, and the number of comic books accounted for 80% How many comic books do you buy?

Set up to buy x comic books
3600*30%+X=（3600+X）*40%
1080+X=1440+0.4X
0.6X=360
X=600
So I bought 600 comic books

There are 210 books in the library of a school, of which 5 / 7 are new books. After purchasing a batch of new books, the ratio of the number of new books to the number of current books is 4:5. How many new books are there
Why use 5x (150 + x) and 4x (210 + x)

Original book 210 * 5 / 7 = 150
I bought X
The current book is 150 + X
The original book is 210
The existing books are 210 + X
therefore
(150+X):(210+X)=4*5
5(150+X)=4(210+X)
750+5X=840+4X
X=840-750=90

When two vehicles transport goods from a certain place to the construction site of 165 dry meters at the same time, Party A arrives 0.8 hours earlier than Party B. when Party A arrives, Party B still has 24 kilometers. How long does it take for Party A to complete the whole journey?

Car B runs 24 kilometers in 0.8 hours,
The speed of car B is 24 / 0.8 = 30 km / h,
When vehicle B travels 165 km, it takes 165 / 30 = 5.5 hours,
It takes 5.5-0.8 = 4.7 hours for car a to complete the whole journey

If a is 20% larger than B and B is 25% larger than C, then a is larger than C () a.40% b.50% c.60% d

A. According to the meaning: A-B = 20% ab-c = 25% B, then a-c = 20% A-25% B, from A-B = 20% a to B = 80% a, then a-c = 40% a“

Is the train fast or the car fast?
What are their average speeds?
When comparing the speed of five modes of transportation in senior one, some data put the speed of the train as the second, while others put the speed of the car as the second. Which one is correct?

As shown in the figure, △ ABC, ab = AC, ad is the high line on the edge of BC, be ⊥ AC, perpendicular foot is e, if ∠ BAC = 45 °, then ∠ EDC=

Because AB = AC, ad ⊥ BC
So D is the midpoint of BC
Because be ⊥ AC
So de = DC
Therefore, EDC = BAC = 45 degree

The average speed of a car travelling from a to B is 40 kilometers per hour. The average speed of the two cars is 60 kilometers per hour

(40+60)/2=50
The average speed of the car is 50 km / h

When k = () the sixth power of formula X - the fourth power of KX, the third power of Y - the ninth power of 4x + the fourth power of 3x + 3, after merging the same inner term, the third power of Y without X

The sixth power of X - the fourth power of KX, the third power of Y - the ninth power of 4x + the fourth power of 3x + 3
=The sixth power of X + (3-K) the fourth power of X, the third power of y-the ninth power of 4x
If not, the coefficient is 0
So 3-K = 0
k=3

The road between a and B is 375 kilometers long. A car has driven 15 kilometers in the first two hours from A. how many hours will it take
To solve by proportion

15:2=375：（X+2）
X=48

Given the equation: x3-3x2 + (M + 2) x-m = 0, the three unequal real roots are the lengths of the three sides of a triangle, then the value range of real number m is ()
A. 0＜m＜1B. m＞34C. 34＜m＜1D. 1＜m＜43

∵ x3-3x2 + (M + 2) x-m = (x3-x2) - [2x2 - (M + 2) x + M] = X2 (x-1) - (2x-m) (x-1) = (x-1) (x2-2x + m) = 0, ∵ X-1 = 0 or x2-2x + M = 0, ∵ there are three unequal real roots of 1, ∵ x3-3x2 + (M + 2) x-m = 0, ∵ x2-2x + M = 0, there are two unequal real roots of the length of the three sides of a triangle, ∵ △ = (- 2) 2-4m > 0, the solution is: m < 1, let x1, X2 be If x 2-2x + M = 0, then x 1 + x 2 = 2, x 1 · x 2 = m, X 1-x 2 = (x 1 + x 2) 2-4x1, x 2 = 4-4m, ∫ x 1-x 2 | 1, ∫ 4-4m | 1, the solution is m ＞ 34, and the value range of real number m is 34 ＜ m ＜ 1

The school library originally had 3600 books, 30% of which were comic books, and the rest were science and technology books. Later, it bought a batch of comic books, and the number of comic books accounted for 80% How many comic books do you buy?