2013.11. 1. When the price of a book is $360, the profit is 25% of the price. If the book is sold at a 20% discount, what is the new profit? 2. Find the standard deviation of 2A + 2, 2A + 4, 2A + 6 and 2A + 8

1 360 * 0.25 = 90 purchase price 270 profit 90 yuan discount 360 * 0.8 = 288 profit 18 yuan
2 2A + 2 + 2A + 4 + 2A + 6 + 2A + 8 = 8A + 20 standard deviation = root 8A + 20

2013.11.19 math problem
1. 75% of a bottle of disinfectant liquor is alcohol, and the rest is water. If 3 liters of water is added, the alcohol content will be reduced to 45%. Calculate the original volume of the bottle of disinfectant liquor
2. The cost of coloring a cylinder with radius R and height h varies with its total surface area. When r = 4 and H = 6, the cost is $20. If r = 8 and H = 14, find the cost

1. Let the original volume be x liter, then x * 75% / (x + 3) = 45% 75X = 45 (x + 3) 75X = 45x + 13530x = 135, x = 4.5 liter. A: the original volume is 4.5 liter. 2. The surface area of the cylinder is s = 2 π RH + 2 π RR. With the increase of the surface area, the cost of R = 8 and H = 14 is x, then S1 / S2 = 20 / x, x = 20 *

In the following real numbers, the irrational number is ()
A；0 B；√5 C；³√8 D；- 22/7
On the number axis, point B and point C are symmetric with respect to point A. if the real numbers corresponding to a and B are √ 3 and - 1 respectively, then the real number corresponding to point C is_____
A_ B C_
-1 0 √3

1、B
2、1+√12

Math problem (our final paper of grade one)
The length of car a is 180 meters, and that of car B is 120 meters. It takes 3 minutes for car a to chase car B, from the front of car a to the rear of car B to leave the front of car B. It takes 20 seconds for car a and car B to walk in opposite directions, from the front of car a and car B to the rear of car a and car B to leave the front of car B
(it's better to explain the detailed process)

If car B is regarded as stationary, then when car a overtakes car B, the speed of car a relative to car B is v A-V B. from car a's head to car B's tail to car a's tail leaving car B's head, the distance of car a relative to car B's head (regarded as stationary) changes 180 + 120 = 300 meters (the drawing is very clear)
Let v a be x, v b be y, 300 / (X-Y) = 3 * 60
Similarly, when two cars are moving in opposite directions, the speed of car a relative to car B is v a + V B
From the front of the car to the rear of the car, the distance between the front of car a and the front of car B has changed by 180 + 120 = 300 meters
300/(X+Y)=20
The solution of binary linear equations is x = 25 / 3, y = 20 / 3

Let's all come in
In the medical insurance of the insurance company, patients who are hospitalized enjoy segmented reimbursement. The reimbursement rules formulated by the insurance company are shown in the table below. The reimbursement amount of someone who is hospitalized is 1120 yuan
Reimbursement rate of inpatient medical expenses (yuan) (%)
Part 0 up to 500
If the part of RMB 500-1000 is more than RMB 60, the medical expenses of this person in hospital are as follows:
Over RMB 1000-3000
A1000 B1250 C1500 D2000

Set the medical expenses as X
If 500

Math problems on the test paper
The equation 3x-5y = 2 is expressed by an algebraic expression containing x, and the form of Y is The form of X is_ .

The equation 3x-5y = 2 is expressed by an algebraic expression containing x, and the form of Y is y = (3x-2) / 5;
The algebraic expression of X with y is x = (5Y + 2) / 3

For a project, it takes 12 hours for Party A to do it alone, 18 hours for Party B to do it alone, and 1 hour for Party A and Party B to work together, then Party A works for 1 hour, and Party B works for 1 hour How many hours will it take to complete the task if two people work alternately like this?

[1 - (112 + 118)] / (112 + 118) = [1-536] / 536, = 3136 / 536, = 615 (round). (536 × 15) / 112 = 136 / 112, = 13 (hours). 6 × 2 + 13 + 1 = 12 + 13 + 1, = 1313 (hours). A: it will take 1313 hours to complete the task

Once, Zhao Kun, Li Dan and Wang Fei combined a taxi (not counting the starting price), and everyone agreed that the taxi fee must be shared reasonably. Zhao Kun got off at one third of the whole journey, and Li Dan got off at two-thirds of the journey. Finally, Wang Fei took a taxi to the terminal and paid 180 yuan. How could the three of them bear the most reasonable fare?

If the whole process is divided into three parts, then: Zhao Kun takes one part, Li Dan takes two parts, and Wang Fei takes three parts
As mentioned above, three people sit 1 + 2 + 3 = 6 pieces of length, a total of 180 yuan, then each price is 80 / 6 = 30 yuan
So Zhao Kun should spend 30 * 1 = 30 yuan, Li Dan should spend 30 * 2 = 60 yuan, Wang Fei should spend 30 * 3 = 90 yuan

The math problems on the test paper
Li Ming drank 1 / 4 of a liter of pure juice for the first time and filled it up with water. He drank 1 / 4 of it for the second time. How many liters of pure juice are left? (score calculation)

The first time left: 1-1 / 4 = 3 / 4
The second time, the remaining 3 / 4 * 3 / 4 = 9 / 16 (L)
A: there are still 9 / 16 liters of pure juice left

480 pairs of sports shoes were shipped from the shopping mall and packed in 2 iron boxes, 3 wooden boxes and 8 cartons respectively. If there are as many sports shoes in 4 cartons as in 1 wooden box, and the sports shoes in 3 wooden boxes can just be packed in 2 iron boxes, then each iron box can be packed with sports shoes______ Double

Let x pairs be packed in each iron box, y pairs in each wooden box and Z pairs in each carton. According to the meaning of the question, we can get the equation: 2x + 3Y + 8Z = 480, ①; 4Z = y, ②; 3Y = 2x, ③; from ② we can get: z = Y4, substituting it into ① we can get: 2x + 5Y = 480, ④; from ③ we can get: y = 23x, substituting it into ④ we can get: 2x + 103x = 480163x = 480, x = 90, answer: 90 pairs of sports shoes are packed in each iron box

2013.11. 1. When the price of a book is $360, the profit is 25% of the price. If the book is sold at a 20% discount, what is the new profit? 2. Find the standard deviation of 2A + 2, 2A + 4, 2A + 6 and 2A + 8