When using A4 paper to copy a document in a transcription agency, if the number of pages is less than 20, the charge for each page is 0.12 yuan. When the number of pages is more than 20, the charge for each page is reduced to 0.09 yuan. When copying the same document in a library, no matter how many pages are copied, the charge for each page is 0.1 yuan, and the charge for each page is 0.1 yuan?

When using A4 paper to copy a document in a transcription agency, if the number of pages is less than 20, the charge for each page is 0.12 yuan. When the number of pages is more than 20, the charge for each page is reduced to 0.09 yuan. When copying the same document in a library, no matter how many pages are copied, the charge for each page is 0.1 yuan, and the charge for each page is 0.1 yuan?

Let X be equal
20*0.12+0.09*(x-20)=0.1x;
2.4+0.09x-1.8=0.1x;
0.01x=0.6;
x=60;
So the price is the same for 60 copies

It's due tomorrow. It's urgent
There is a sum of money. If you buy class a goods alone, you can buy 150 pieces. If you buy class B goods alone, you can buy 90 pieces. Now you have bought 100 pieces of class A and class B goods with this money. How many pieces of class A and class B goods have you bought?
A bookstore promotes sales by the way of "20 yuan membership card enjoys 20% discount". Under what circumstances do you think it is cost-effective to apply for membership card

(1) Set: this money is 1, buy a x pieces
（1/150）x+（1/90）（100-x）=1
If x = 25, then 100-x = 75
(2) It is appropriate to apply for membership card when the consumption is set at x yuan
20+ 80%×x≤x
If the solution is x ≥ 100, then more than 100 yuan is appropriate

Xiao Ming finished reading a 96 page story book in two days. On the first day, he read 3 / 5 of the total pages. On the second day, how many pages did he read~~

96×（1-3/5）＝192/5

Given the set M = {0, 1, 2}, n = {x | x = 2a-1, a ∈ n *}, then the set M ∩ n = ()
A. {0}B. {1，2}C. {1}D. {2}

N={x|x=2a-1，a∈N*}={1，3，5，7，9，… }And M = {0, 1, 2}, ∩ m ∩ n = {1}, so C

When someone travels for 22 days, he takes the train, the car and the bicycle walk one third of each other. The speed of the bicycle is 1 / 8 of the speed of the train and 1 / 4 of the speed of the car,
How many days by train, car and bike?

If the train ride is x days, the car ride is y days, and the bicycle ride is Z days, and the total distance is s, then
X+Y+Z=22 ,8/Z=1/X=2/Y,
The solution is x = 2
Y=4
Z=16
A: 2 days by train, 4 days by car and 16 days by bike

It is known that there is no XY in the difference between the square plus my minus 12 of the polynomial 2x and the square minus 3Y plus 6 of the polynomial NX

If there is no X, y, it means that the two terms are subtracted, and the formulas with X, y cancel each other, so n = 2, M = - 3, then M + N + Mn = - 7

Mathematical problems about speed, time and distance
Xiaohua is walking along the roadside. Every ten minutes, a car passes behind him. Every eight minutes, another car comes from the front. Xiaohua and the car drive at a constant speed. How often does the station run?

If the speed of passenger car is a kilometer per hour and that of freight car is B kilometer per hour, and the distance between a and B is m kilometer, then
10a=15b,b=2a/3
[M / (a + b)] * a + 96 = 80% * m, substituting B = 2A / 3 into the solution, M = 480
Respondent: the public in 2009

The equation with only one (), the degree of unknowns is (), and both sides of the equal sign are (), is called one variable linear equation

Unknowns

The universe is in a vacuum. The spaceship has no resistance in the vacuum. Why can it change its flight direction?
Some people say that it is propelled by the gas ejected from the spaceship pushing the gas ejected before, but the gas ejected before has the same speed as the gas ejected after, that is, it is relatively static and has no resistance. Can it fly like this?

Conservation of momentum

Please write a system of quadratic equations with X and y as unknowns, and satisfy the following two conditions at the same time
(1) The solution of (2) system is {x = 2
{y=3
Such a system of equations can be ()

x+1=y
2x-1=y