Three fifths of four ninths are closest to A. one third B. one fourth C. one fifth

Three fifths of four ninths are closest to A. one third B. one fourth C. one fifth

B. A quarter
Four out of nine and three out of five are 4 / 9 * 3 / 5 = 12 / 45
1/3=12/36
1/4=12/48
1/5=12/60
The closest is B. quarter

One third of a number is four ninths, which is a fraction of six

4/9÷1/3÷6=2/9

Class 61 has 40-50 students, two fifths more boys than girls. How many boys and girls are there in this class?

If there are x girls, there are 7 / 5x boys
40≤7/5x+x≤50
The solution is 50 / 3 ≤ x ≤ 125 / 6
So there may be 17-20 girls, because only 20 is a multiple of 5, so there are 20 girls and 28 boys
Because I don't know what grade you are, I don't know if you can understand this practice~~

The students of class 61 are between 40 and 50, and the number of girls is one fifth more than that of boys. How many boys and girls are there in this class?

Female students are the standard quantity, while female students are the standard quantity
Boys: 1 + 1 / 5 = 6 / 5
6 / 5 + 1 = 11 / 5
Then the class number must be a multiple of 11, between 40 and 50, then the class number is 44
Female: 44 △ 11 / 5 = 20 (person)
Male: 44-20 = 24

Which cuboid or cylinder below is bigger? (unit: cm)
The circumference of the cylinder is 25.12 square centimeters, the height is 6 centimeters (vertical), the cuboid is vertical; the height is 6 centimeters, the length and width are 8

The volume is equal to the base area times the height
It's all six centimeters high
So compare the bottom area
Circle radius 25.12 ÷ 2 ÷ 3.14 = 4cm
Bottom area 3.14 × 4 × 4 = 50.24 square centimeter
Rectangular bottom area 8 × 8 = 64 square centimeter
So the cuboid is big

Simple calculation of 54 times 99 + 54

54 times 99 + 54
=54*（99+1）
=54*100
=5400
[questions are welcome]

The proof (1) when x > 1, e ^ x > ex needs to use Rolle's theorem

Let f (x) = e ^ x-ex
f‘（x）=e^x-e
x> Simple increment of 1 e ^ x > e f '(x) > 0 function
So f (x) > F (1) = 0

The density p (kg / m ^ 3) of a certain mass of gas is the inverse proportional function of its volume V (m ^ 3). It is known that when v = 8 (m ^ 3), P = 1.45 (kg / m ^ 3), then the value of P is obtained when v = 9

(8*1.45)/9=1.2889

If the new operation is defined as a ∇ B = a + 1b, then the value of 2 ∇ (3 ∇ 4) is______ ．

∫ the new operation is defined as a ∫ B = a + 1b, ∫ 3 ∫ 4 = 3 + 14 = 1 ∫ 2 ∫ (3 ∫ 4) = 2 + 11 = 3

Some people went to do voluntary labor. They originally arranged 80 people to transport the soil and 52 people to dig up the earth. Now the number of people who need to carry the earth is 3 times the amount of earth digging, so that the dug can be transported away. Then how many people should be transferred from the excavators to the earth?
I understand it as follows:
Set up the X people to remove the soil from the excavators.
80 + X (all people) = 3 (52-x) (multiply the rest by 3)
Why is the calculation wrong?

You did exactly the right thing
Set up the X people to remove the soil from the excavators.
80 + X (all people) = 3 (52-x) (multiply the rest by 3)
The solution
80+x=156-3x
4x=156-80=76
x=19
19 people should be transferred from the earth digester to the earth.