If a bookstore sells a new book at a 10% discount on its price, it can still make a profit of 4.2 yuan. If the purchase price of the book is 21 yuan, the price is () yuan

If a bookstore sells a new book at a 10% discount on its price, it can still make a profit of 4.2 yuan. If the purchase price of the book is 21 yuan, the price is () yuan

(21 + 4.2) / 0.9 = 28 yuan

Xinhua Bookstore bought a batch of new books. One third of them were sold in the first day, 40% in the second day, and 200 more than the first day, two days later
How many copies are left in the future?

In total:
200 (40% - 1 / 3) = 3000 copies
Remaining "3000 × (1-40% - 1 / 3) = 800 copies
Answer: there are 800 copies left

There are 600 new books in Xinhua Bookstore, 192 in the morning and 249 in the afternoon. How many are left?

600 - (192 + 249), = 600-441, = 159 (copies); a: there are 159 copies left

To solve the equation 3 / x-1-2 / 4-x = 1 without denominator is correct

(x-1)/3 -(4-x)/2=1
Multiply both sides by 6,
2(x-1)-3(4-x)=6,
Sorting, shifting:
2x-2-12+3x=6,
5x=20,
x=4

If 24 tons of grain are transported from warehouse A to warehouse B, the amount of grain stored in two warehouses will be 1 / 5 more than that in warehouse B

Your question is: the tonnage of grain stored in warehouse A is 1 / 5 more than that in warehouse B. If 24 tons are transported from warehouse A to warehouse B, then the two warehouses have the same amount of grain stored. Find the amount of grain stored in the two warehouses
If the stock quantity of warehouse B is x, the stock quantity of warehouse A is 6 / 5x
6/5x-24=x+24
6/5x-x=24+24
1/5x=46
x=46x5
x=230
So the inventory of warehouse A is 6 / 5x230 = 276 (tons)
Answer: a warehouse inventory is 276 tons, B warehouse inventory is 230 tons

What is a number if 40% of it is exactly equal to the product of 20 and half? (solve the equation)

0.4x=20*0.5
x=25

Here's a math problem
Mr. Wang deposits a sum of money in the bank and withdraws it as a whole for five years, with an annual interest rate of 3.60%. When it is due, he donates 50% of all the interest to "Hope Primary School", and the rest to the welfare home. The welfare home receives Mr. Wang's donation of 4500 yuan. How much is the sum of money Mr. Wang deposited in the bank?

（4500×2）÷（5×3.60%）
=9000÷0.18
=50000 yuan
A: Mr. Wang deposited 50000 yuan in the bank

It is known that the sequence an is an equal ratio sequence, its common ratio is a positive number, and A2 = 2, S3 = 7

a2=a1q=2
S3=a1(1-q^3)/(1-q)=a1(1+q+q^2)=7
a1+2+2q=7 a1=5-2q
5q-2q ^ 2 = 2 2q ^ 2-5q + 2 = 0 (2q-1) (Q-2) = 0, q = 1 / 2 or 2A1 = 4 or 1
an=4*(1/2)^(n-1)=(1/2)^(n-3)
Or an = 2 ^ (n-1)

3.8 * 3.9 + 5.1 * 3.8 + 3.8 by simple method

3.8*3.9+5.1*3.8+3.8 =3.8*（3.9+5.1+1）=38

As shown in the figure, A1 (1,0), A2 (1,1), A3 (- 1,1), A4 (- 1, - 1), A5 (2, - 1) What is the coordinate of a2007
Come on

It can be seen from the figure and narration that each point (except A1 point) is located on the bisector of the four quadrants,
The subscripts of the letters corresponding to the point of the bisector of the first quadrant are 2,6,10,14,
That is 4n-2 (n is a natural number, n is the absolute value of the abscissa of the point);
Similarly, the subscript of the point in the second quadrant is 4N-1 (n is a natural number, n is the absolute value of the abscissa of the point);
The third quadrant is 4N (n is a natural number, n is the absolute value of the abscissa of the point);
The fourth quadrant is 1 + 4N (n is a natural number, n is the absolute value of the abscissa of the point);
2007 = 4N-1, then n = 502. When 2007 equals 4N + 1 or 4N or 4n-2, there is no such value of n
So point a2007 is on the angular bisector of the second quadrant, that is, the coordinate is (- 502)
So fill in the answer (- 502)