A passenger car and a freight car are running in the same direction on the parallel track. The passenger car is behind the freight car. The length of the passenger car is 200 meters and the length of the freight car is 280 meters. The ratio of the speed of the passenger car and the speed of the freight car is 5:3. The crossing time for the passenger car to catch up with the freight car is 1 minute. The speed of each car is calculated. If the two cars are running in opposite directions, what is their crossing time?

Suppose the speed of passenger car is 5x M / min and that of freight car is 3x M / min, then there is: 5x = 3x + 280 + 200, and the solution is x = 240. Therefore, the speed of passenger car is 5 × 240 = 1200 (M / min), and that of freight car is 3 × 240 = 720 (M / min). If two cars are running in opposite directions, then the crossing time is (280 + 200) / (1200 + 720) = 0.25 (min) = 15 seconds Five seconds

There is a barge with a carrying capacity of 800 tons and a volume of 795 cubic meters. Now it is carrying pig iron and cotton. The volume of pig iron per ton is 0.3 cubic meters, and that of cotton per ton is 4 cubic meters. How many tons of pig iron and cotton can we make full use of the carrying capacity and capacity of the barge?

Suppose the pig iron transports x tons, then the cotton transports (800-x) tons. From the meaning of the question, we can get: 0.3x + 4 (800-x) = 795, the solution is: x = 650800-650 = 150 (tons). Answer: the pig iron transports 650 tons, and the cotton transports 150 tons

How much is 422-101 × 422

422-101*422
=422（1-101）
=422*（-100）
=-42200

How to derive an equation with absolute value?

According to the definition field given by the topic, the interval is divided according to the expression within the absolute value and the value of 0, and the absolute value number is removed. If the definition field is not given clearly, it is generally divided according to the real number interval

1、 In a one minute rope skipping competition, the scores of 12 students are as follows: 52 36 47 45 50 53 48 46 49 44 51 55
1. Arrange the data from small to large
2. What are the median and average of this group of data?
3. Which number is more suitable to represent the general level of this group of data?
4. Add a classmate Liu Dan, her score is 52, what is the median of this group of data?

1. Arrange the data from small to large
thirty-six

Three fifths of a number is 28 less than two times his. What's the number

Hongwowo:
Let this number be x, and the equation is as follows:
3x／5+28＝2x
Multiply each item by 5 to get:
3x+140＝10x
140＝7x
x＝20
A: the number is 20
Good luck and goodbye

Dividing X / x ^ 2-1 and 2 / x ^ 2 + 2x + 1
1 / x ^ 2-y ^ and 1 / x ^ 2 + XY

1.
The simplest common denominator is (x + 1) ^ 2 (x-1)
x/(x^2-1)=x(x+1)/(x+1)^2(x-1)
2/(x^2+2x+1)=2(x-1)/(x+1)^2(x-1)
two
The simplest common denominator is x (x + y) (X-Y)
1/(x^2-y^2)=x/x(x+y)(x-y)
1/(x^2+xy)=(x-y)/x(x+y)(x-y)
If you don't understand, please ask, I wish you a happy study!

How to calculate 102 * 4.5

(4+0.5)*102 = 4*102 + 0.5*102 = 408 + 51 = 459
Or split 102 into (100 + 2)
This kind of problem depends on the specific situation, which is convenient to dismantle which

The limit of [(1 + MX) ^ n - (1 + NX) ^ m] / x ^ 2 (x tends to 0)
The reference answer is Mn (n-m) / 2
How can I find the derivative of (1 + MX) ^ n? I'm too stupid

Continuous use of the law of lobita: because it is the form: 0 / 0.the limit of [(1 + MX) ^ n - (1 + NX) ^ m] / x ^ 2 (x tends to 0) = m ^ 2n (n-1) (1 + MX) ^ (n-2) - Mn (m-1) (1 + NX) ^ (m-2) (x - > 0) = m ^ 2n ^ 2-m ^ 2-m ^ 2n + Mn (1 + MX) ^ n how to find the derivative is = n (1 + MX) ^ (n-1) (1 + MX) '= M

Given that x = - 5 is the root of the equation AX + B = 0, find the value of - 5A + B-2

It is known that x = - 5 is the root of the equation AX + B = 0
Then - 5A + B = 0
Then - 5A + B-2 = - 2