Eighth grade "happy summer vacation" mathematics answer, Beijing Normal University Edition, some questions can't, I have already finished. Thank you 1. In order to alleviate the traffic pressure in the city center, a city plans to build a railway across the East and the West. In order to complete the project three months ahead of schedule, the original work efficiency needs to be increased by 12%. How many months does the original plan take to complete this plan? 2. There are two engineering teams a and B to build a section of expressway. If a and B cooperate, it will take 24 days, and the cost is 1.2 million yuan, (1) how many days does it take for team a and team B to complete the project independently? (2) how much does it cost for team a and team B to complete the project independently? [please write down the specific process]

1. It is supposed to take x months to finish the project
one
------------- +3 =X
（1+12%）*（1/X）
one
------------- +3 =X
1.12/X
X
------------- +3 =X
one point one two
X+3*1.12=1.12X
X+3.36=1.12X
X-1.12X=-3.36
-0.12X=-3.36
X=28
A: it was originally planned to take 28 months to complete the project
2. (1) the working efficiency of team a is x, and that of team B is y
24(X+Y)=1 ①
20X+40Y=1 ②
From 1
X=1/24-Y ③
Substitute (3) for (2)
20*(1/24-Y)+40Y=1
The solution is y = 1 / 120
The y = 1 / 120 generation can be obtained
X=1/24-1/120=4/120=1/30
So it takes team a [1 / x = 1 / (1 / 30) = 30] days to complete the project alone, and team B [1 / y = 1 / (1 / 120) = 120] days to complete the project alone
A: it takes 30 days for team a to complete the project alone, and 120 days for team B to complete the project alone
(2) Team a alone costs a million per day, team B alone costs B million per day
24*（A+B）=120 ① ①②③④⑤⑥⑦
20*A+40*B=110 ②
From 1
A=5-B ③
Substitute (3) for (2)
20*（5-B）+40*B=110
The solution is b = 0.5
Substitute B = 0.5 into 3 to get
A=5-0.5=4.5
So team a needs (4.5 * 30 = 1.35) million to complete the project alone, and team B needs (0.5 * 120 = 60000) million to complete the project alone
A: it costs 1.35 million for team a to complete the project alone, and 600000 for team B to complete the project alone

Published on 12 may 2012

There are all the summer homework answers of junior high school in 2012 in the answer network of thought island

Fill in the blank (1) a cylindrical iron bucket with a volume of 502.4 liters, with a bottom diameter of 0.8 meters and a height of () meters
Aunt Wang uses a rectangular red cloth with a length of 8 meters and a width of 1 meter to make a triangular red flag with two right angles of 1 decimeter on each side. How many small red flags can this red cloth make?
I am anxious. By the way, I will write another composition and a letter to the future teacher. Points will be awarded to those who meet the requirements and are the fastest!

Dear future teacher: I am a classmate of grade 6 in primary school. In half a year, I will graduate from primary school. Although we have never met each other, I want to give you some suggestions. First of all, I hope you can standardize the language, respect others, and understand the students' inner thoughts. Sometimes some students are not studying or doing something wrong, please use

49 and seventeen eighteenth times nine,

44 and 9 / 18

As shown in the figure, the constant power supply voltage is u = 14 V, the small bulb L is marked with "4 V, 8 W", and the coil resistance of the motor RM = 1 Ω. When the rheostat is adjusted to 2 Ω, the,
The small light bulb and the motor work normally, and the mechanical efficiency of the motor (three things in series)

I=P/U=8/4=2A
Rheostat voltage U = IR = 2 * 2 = 4V
Voltage drop of motor u = 14-4-4 = 6V
Total power of motor = IU = 2 * 6 = 12W
Electric heating power of motor = I ^ 2R = 2 ^ 2 * 1 = 4W
Mechanical efficiency = (12-4) / 12 = 67%

1 / 2 - (0.875 * 2 / 13 + 1 / 6.5 / 8) * 1 and 6 / 7

1 / 2 - (0.875 * 2 / 13 + 1 / 6.5 / 8) * 1 and 6 / 7
=1/2-[（7/8)*(2/13)+(2/13）*（1/8）]*（13/7）
=1/2-[(2/13)*(7/8+1/8)]*(13/7)
=1/2-(2/13)*(13/7)
=1/2-2/7
=7/14-4/14
=3/14

How many kwh is 6800 kwh

1 kwh = 1 degree
6800 kwh is equivalent to 6800 kwh

The sixth grade of primary school Volume II on the application of proportion problems
The area of a rectangle reduced by 1:3 is 0.36 square meters. How many square meters is the original area of the rectangle?

3.24

Incandescent lamp is a pure resistor that can emit light and heat. So it generates heat energy and light energy by consuming electric energy. Does this light energy belong to internal energy or contained in internal energy?
Does this light energy belong to internal energy or is it contained in internal energy,

On the second floor, the description of energy conversion process is very correct. However, it fails to answer the question of the building owner
Deltau = w + Q, the light energy (and "heat energy") released by the bulb is the release of heat, resulting in the reduction of the internal energy of the bulb. If the external (power supply) is considered to do electrical work, the internal energy of the bulb will remain unchanged after the stable lighting, and the electrical work will be converted into heat and distributed to the outside, When the light and heat are absorbed by the surrounding objects, "light and heat" do not exist and become the internal energy of the surrounding objects
The energy of the light and heat that are being transmitted does not belong to any physical object, but belongs to the photon or electromagnetic wave that transmits energy. Therefore, it does not belong to internal energy, only belongs to heat

758 & # 178; - 258 & # 178; calculated by square difference formula

(758+258)(758-258)
=1016×500
=508000