Positive proportion and negative proportion 1. A has 150 grey rabbits, white rabbits and black rabbits. The number of white rabbits is 5 / 6 of that of black rabbits. The ratio of black rabbits to white rabbits is 4:5. How many grey rabbits are there? 2. For a classroom, 800 pieces of brick with a side length of 3DM should be used. If the brick with a side length of 4dm should be used, how many pieces should be used? 3. Fill in the blanks according to the proportion A 8 12 （ ） 2 24 （ ） B 6 4 15 （） （） 48

Positive proportion and negative proportion 1. A has 150 grey rabbits, white rabbits and black rabbits. The number of white rabbits is 5 / 6 of that of black rabbits. The ratio of black rabbits to white rabbits is 4:5. How many grey rabbits are there? 2. For a classroom, 800 pieces of brick with a side length of 3DM should be used. If the brick with a side length of 4dm should be used, how many pieces should be used? 3. Fill in the blanks according to the proportion A 8 12 （ ） 2 24 （ ） B 6 4 15 （） （） 48

(1) White rabbit: black rabbit = 5:6, gray rabbit: white rabbit = 4:5, black rabbit: gray rabbit: white rabbit = 10:12:15
150/(10+12+15)*10=
(2):8 12 (3) 2 24 (36)
(3):6 4 15 (10) (72) 48

The wealth is high
A batch of yellow sand has been transported for 84 tons in the first seven times. According to this calculation, the task has been completed for 25 times. How many tons are there in total?
It takes 6000 sheets of paper to bind 200 exercise books. At present, there are 15000 sheets of paper. How many of the same exercise books can be bound?
It takes 2000 pieces to lay a piece of land with 20 cm long square bricks. If you use 40 cm long square bricks, how many pieces do you need?

1. Suppose that there are x tons of yellow sand in total. 84:7 = x: 257x = 25 × 84x = 300 a: there are 300 tons of yellow sand in total. 2. Suppose that the same exercise book x can be bound. 6000:200 = 15000: x600x = 200 × 150000x = 300000 △ 60000x = 500 a: the same exercise book 500 can be bound. 3

Use three of the four numbers 5, 10, 20 and 40 to make up a positive proportion problem first, and then make up an inverse example to solve it

Positive proportion: Xiao Wang makes 10 parts in 5 days, how many parts can he make in 20 days?
Inverse proportion: to fill a warehouse with goods, it takes 40 days to employ 5 workers, and how many days to employ 20 workers?

Fourth grade volume 2 Mathematical oral problems

640÷80= 15×5= 23×3= 12×2×5= 480÷80= 16×5= 27×3= 90÷15= 48÷4= 640÷16= 39÷3= 24×20= 32×3= 48÷16= 12×8= 27×3= 56÷14= 24÷8= 14×2= 83－45= 560÷80= 96÷24= 40÷20= 40×30= 37＋26= 76－3...

General solution of differential equation XY '- 2Y = 2x ^ 4
Convergence and divergence of discriminant series (∞Σ n = 1) n ^ 2 / 3 ^ n

xy'-2y=2x^4
y'-2y/x=2x^3
Apply the formula
Normally:
y'+p(x)y=q(x)
Then the formula of the solution is as follows:
y=e^[-∫p(x)dx]{∫q(x)*e^[∫p(x)dx]dx+C}
=e^[-∫(-2/x)dx]{∫2x^3*e^[∫(-2/x)dx]dx+C}
=x^2(∫2x^3/x^2dx+C)
=x^2(x^2+C)

1 g / cc = how many kg / m3

1 g / cc = 1000 kg / m3

Twelve nines add, subtract, multiply and divide equal 1212,
Urgent

[（9 + 9）÷ 9 + 9 × 9 + 9 + 9 ] × [（9 + 9 + 9）÷ 9 + 9]
=101 × 12
=1212

The area of the triangle formed by the line y = 3x + 6 and the two coordinate axes is ()
A. 6B. 12C. 3D. 24

Let the coordinates of the intersection of the line and the x-axis be a (x, 0), and the intersection of the line and the y-axis be B (0, y). Substituting a and B into the analytical formula, we can get x = - 2, y = 6. Therefore, the coordinates of a and B are a (- 2, 0), B (0, 6). So s △ ABC = 12 × 2 × 6 = 6

A cylinder has a side area of 12 square meters and a radius of 2 meters

The derivation process of cylinder volume: the cylinder is cut and then assembled into a cuboid. Half of the side area of the original cylinder is used as the bottom of the cuboid, and the radius of the bottom of the cylinder is used as the height of the cuboid
12 △ 2 × 2 = 12 cubic meters

3, - 5,2, - 13 are 24 points

1: 3 + 2 × (-13) +(- 5)
2: 3 × 2 + (-13) + (-5)