After Xiaoqiang joined the school sports training team, the time of running 100 meters was shortened from the original 18 seconds to 15 seconds, and the speed of Xiaoqiang's 100 meters was increased by how many percent? (one decimal place before the percent sign)

(100 / 15-100 / 18) / (100 / 18), = (203-509) / (509, = 109 / 509, = 20%); a: the speed of forced running 100 meters is 20% higher than the original

It takes 18 seconds for Xiaolin to run 100 meters and 15 seconds for pony to run 80 meters, so Xiaolin's speed is faster than pony's () A. B. slower than pony's () C. same as D. can't be sure

Xiao Lin's speed is 100 / 18, Xiao Ma's speed is 80 / 15

5 years 2 class P.E. class line up, the teacher found that the class students line up 2 lines, the team more than 1 person, line up 3 lines more than 2 people, 4 lines more than 3 people, 5 lines more than 4 people, how many people in the class

Suppose there are x people in the class
(x + 1) is the common multiple of 2,3,4,5
So at least x + 1 = 60
X=59
So there are at least 59 students in this class
PS should be the least, otherwise there are countless answers~

A bottle with a volume of 300 cubic centimeters contains 200 grams of water. A thirsty crow takes some water with a density of 1
A bottle with a volume of 300 cubic centimeter contains 200 g of water. A thirsty crow puts some pebbles with a density of 2.5 g / cubic centimeter into the bottle. (1) what is the total volume of pebbles that the crow needs to put into the bottle to make the water level rise to the bottle mouth? (2) what is the total mass of pebbles put into the bottle?

Volume of water in the bottle: mass / density = 200 cm3
Inside the bottle: 300 cubic centimeter, so the total input of stones should be (300 - 200) = 100 cubic centimeter
According to the mass / volume = density, the total mass should be 100 * 2.5 = 250g
The process is given, the best one is given,

After mixing 50 cubic centimeter of water and 50 cubic centimeter of alcohol, the total mass of the mixture is 90 g, then the density of the mixture is 90 G
Then the density of the mixture (select "less than", "greater than" and "equal to") is 0.9x10 cubic kg / m3
This is the third year of junior high school. Please write down the process of how to calculate~

After 50 cubic centimeter of water and 50 cubic centimeter of alcohol are fully mixed, the total mass of the mixture is 90 g, then the density of the mixture (fill in "less than", "greater than" and "equal to") is 0.9x10 cubic kg / m3
greater than
The volume of water and alcohol after mixing will be less than the volume of water + alcohol before mixing

It is known that the mass of carbon-12 atom is 1.993 * 10-26kg, and that of a atom is 5.146 * 10-26kg. If the number of neutrons in a nucleus is one more than that of protons
How to find the number of electrons outside the nucleus of atom A?

The relative atomic mass of atom A is obtained by dividing the mass of atom A by one twelfth of the mass of atom C 12, which is approximately regarded as the mass number of atom a,
The number of protons = the number of atoms divided by the mass of protons can reach - 1!

The mass of a carbon atom with six protons and six neutrons in the nucleus is m kg, and the mass of an atom is n kg. Calculate the relative mass of the atom

12/M=m/n
So the relative mass of the atom M = 12n / m

It is known that the mass of a carbon atom (containing 6 neutrons and 6 protons) is 1.993 × 10-26 & nbsp; kg, and that of an oxygen atom is 2.657 × 10-26 & nbsp; kg, then the calculation expression of the relative atomic mass of an oxygen atom is______ ．

The relative atomic mass of oxygen atom = the mass of oxygen atom × 112 = 2.657 × 10 − 26kg 1.993 × 10 − 26kg × 112 = 2.657 × 10 − 26kg × 121.993 × 10 − 26kg

It is known that the mass of an oxygen atom is 2.675 * 10 minus 26kg, then how many oxygen substances are 1mol

1mol = 6.023x10 ^ 23
It has nothing to do with any other quantity

After Xiaoqiang joined the school sports training team, the time of running 100 meters was shortened from the original 18 seconds to 15 seconds, and the speed of Xiaoqiang's 100 meters was increased by how many percent? (one decimal place before the percent sign)