The approximate number is -0.0450, 20000, 20000, 3.14 times the 5th power of 10, and -6.800 times the 4th power of 10. It is accurate to a few digits, a few significant numbers We need it now That's all. Do me a favor

-0450,20 000,
Decile
6 significant numbers
2000,
Thousand
2 significant numbers
14 times 10 to the fifth power,
Thousand
3 significant numbers
-800 times 10 to the fourth power
Thousand
4 significant numbers

430 divided by 70 = 43 divided by 7 = 6 ------ 1, right? If not, how to correct it

No
430 divided by 70 = 43 divided by 7
But 430 divided by 70 = 6 ten

Is Xiao Hong's calculation right? If not, please write the correct formula: 430 ／ 70 = 43 ／ 7 = 6 ···· 1 I know it's wrong
Is Xiao Hong's calculation correct? If not, please write the correct formula:
430÷70=43÷7=6······1
I know it's wrong, but I don't know how to revise it. Who's right,

It should be more than 60

The speed of the earth around the sun is about 1.1 times 10 to the fifth power km / h, and the sound propagation in the air is about 340m / s

340m/s=1224km/h

Problems P37, 9 and 10 in the second volume of the eighth grade of PEP
9: The working efficiency of a harvester is 150 times that of a farmer. It takes one hour less to harvest 10 hectares of wheat with this harvester than 100 farmer workers. How many hectares of wheat does this harvester harvest per hour?
10: A car is going to the destination 180 km away from the starting place. It will drive at the same speed as originally planned within the first hour after departure. After one hour, it will drive at 1.5 times of the original speed and arrive at the destination 40 minutes ahead of the original plan
The answer is 5 hectares, 60 km / h
After the equations are listed, the first step of calculation is to multiply both sides by a number at the same time,

(/ semicolon for fraction)
9. Set the working efficiency of a farmer as X HA / h, and this harvester as X HA / h
10 / 100x - 10 / 150x = 1
Both sides of the equation are multiplied by 150x
15 - 10 = 150x
The solution is x = 1 / 30, 150x = 5
The test shows that x = 1 / 30 is the solution of the original equation
A: This harvester harvests 5 hectares of wheat per hour
10. Set the driving speed of the previous hour as X km / h
From the meaning of the title, 180-x / X - 180-x / 1.5x = 2 / 3
Multiply both sides of the equation by 3x
540-3x-(360-2x)=2x
Merge similar items
180 = 3x
The solution is x = 60
It is proved that x = 60 is the solution of the original equation
A: the speed of the previous hour was 60 km / h

What's the difference between symmetry about the origin and symmetry about the Y axis
If it's symmetric about the origin, is it necessarily symmetric about the Y axis
How to use this symmetry to judge the parity of a function?

About the origin symmetry is about the origin center symmetry,
About Y-axis symmetry is about Y-axis symmetry,
The centrosymmetry of the origin is that the image is rotated 180 degrees based on the origin, and the image before and after the change is the same, so the function of this image is odd,
The y-axis symmetry is to rotate the image 180 degrees with the y-axis as the symmetry axis, and the image before and after the change is the same, so the function of the image is even

7 of 13 * 4 of 17 + 7 of 13 * 9 of 17
What's the formula

7 of 13 * 4 of 17 + 7 of 13 * 9 of 17
=7 out of 13 * (4 out of 17 + 9 out of 17)
=7 out of 13 * 13 out of 17
=7 out of 17

1. Heat 20 g of iron oxide. At the same time, get enough CO to make it react completely. Then, produce CO 2 and pass it into clear lime water. Finally, get 37.5 g of precipitate?
2. One gram of ore sample containing SiO 2 and FeS 2 is taken and fully burned in the oxygen clock. The residual crying mass is 0.84 g. suppose that the sulfur loss is 2% in the reaction process. How many tons of 98% sulfuric acid can be produced from 1000 tons of this ore?
3. 70 g of the mixture of Na 2O and Na 2O 2 is fully reacted with 98 g of sodium hydroxide. The mass percent concentration of the obtained NaOH solution is 50%. Write out the chemical equations respectively. Calculate the mass of Na 2O and Na 2O 2 in the mixture?
When the temperature is 4.200 ℃, 11.6 g of the mixture of CO 2 and steam reacts with enough Na 2O 2, the weight of the solid increases by 3.6 G?

1. Carbon conservation. Ncaco3 = nco2 = NCO = no atom = 0.375 mol
The oxygen atom of CO is obtained from iron oxide, so the amount of iron in iron oxide is (20-0.375 * 16) / 56 = 0.25mol
therefore nFe:nO=2 :3
Fe2O3
2. In order to calculate the amount of sulfuric acid, the content of pyrite must be calculated first,
According to the meaning of the title, if 1 g ore sample contains fes2x g, then:
4FeS2＋11O2=2Fe 2O3＋8SO2 △m
4×120 2×160 160
X 1-0.84 G
X = = 0.48g
The percentage of FeS2 in pyrite is 48%
Suppose that 98% of H2SO4 can be produced, then:
FeS2 2H2SO4
120 196
1000 × 48% × (1-2%) tons y × 98%
Ψ y = = 784 tons
(1) It is calculated according to the concept of solute mass fraction
w(NaOH)＝ ×100%
(2) The calculation is based on the equal mass of solute and solvent in the resulting solution
The reactions were as follows
Na2O+H2O＝2NaOH；2Na2O2+2H2O＝4NaOH+O2↑
Let the mass of Na 2O 2 and Na 2O in the mixture be x and y, respectively
2Na2O2+2H2O＝4NaOH+O2↑；
2×78 2×18 4×40 32
x x x x
Na2O+H2O＝2NaOH
62 18 2×40
y y y
The solution is: x = 39G; y = 31G
Answer: ① 2na2o2 + 2H2O = 4naoh + O2 ↑;
② The original mixture contains 39 g of Na2O2 and 31 g of Na2O2
2na2o2 + 2co2 = 2na2co3 + O2 weight gain
88x 56x
2na2o2 + 2H2O = 4naoh + O2 weight gain
36y 4y
88x+36y=11.6
56x+4y=3.6
x=0.05mol
y=0.2mol
(44*0.05+18*0.2)/(0.05+0.2)=23.2
I'm tired of playing

Given that a triangle and a parallelogram are of equal height, what is the ratio of their areas?

The area of triangle is 1 / 2 bottom * height
The area of a parallelogram is base * height
Because of the equal base and height, the ratio of area is 1:2

How to simplify the calculation of 1.38/1.25

1.38/1.25
=（1.38*8）/(1.25*8)
=11.04/10
=1.104
If it helps you, please take it. Thank you
To adopt the first correct answer is to respect the labor of the respondents. I wish you progress!

The approximate number is -0.0450, 20000, 20000, 3.14 times the 5th power of 10, and -6.800 times the 4th power of 10. It is accurate to a few digits, a few significant numbers We need it now That's all. Do me a favor