When a hollow copper ball with a mass of 89g is suspended in water, the volume of the hollow part of the copper ball is? And the density of copper is 8.9 × 10 cubic kg / M & sup3;

Because the hollow copper ball is suspended in water, f floating = g copper, V ball = V row = m copper / P water = 89cm3, V copper = m copper / P copper = 1cm3, V empty = V ball - V copper = 88cm3

The weight of iron in air is 3.12n, and that in water is 2.5n. Buoyancy, ball volume and whether the ball is hollow (density is 7.9 * 1000kg / m3, G is 10N / kg)

According to Archimedes principle, f floating = P water GV ball P water = 1 * 10-3kg / m3v ball = f floating / P water g = 0.62 / (1 * 10-3 * 10) = 0.000062m3, if the ball is solid, then the mass of V ball of equal volume m = P iron * V ball = 7.9 * 10-3 * 0.000062 = 0.4898kgg ball =

There is a solid iron ball with a weight of 7.9n. When it is immersed in water, what is the volume of boiled water? How buoyant is it? (ρ Fe = 7.9 × 103kg / m3, g = 10N / kg)

∵ g = mg, ∵ M = GG = 7.9n10n / kg = 0.79kg, ∵ ρ = MV, ∵ V iron = m, ρ iron = 0.79kg, 7.9 × 103kg / m3 = 1 × 10-4m3; ∵ when it is immersed in water, then V row = V iron = 1 × 10-4m3; ∵ according to Archimedes' principle, f floating = ρ gvrow = 1 × 103kg / m3 × 10N / kg × 1 × 10-4m3 = 1n

1. Three rectangular wood blocks of 5cm in length, 4cm in width and 3cm in height are used to form a cuboid with the largest surface area. How many square centimeters is the surface area of this cuboid?
2. How many square centimeters will the surface area of a cuboid steel which is 80cm long, 158CM wide and 158CM high be reduced after sawing the largest cube from one end of the steel?
3. The surface of a cube wood block with an edge length of 1 meter is coated with red paint, and then cut into small cubes with a volume of 1 cubic decimeter. How many cubes are painted on both sides and one side respectively?
4. Put two identical cuboid blocks together into a cube, the surface area is 40 square centimeters less than the original. How many square centimeters is the original surface area of each cuboid?
The most important thing is, because I really don't know which one. Also, please help me to write the formula. I can't understand it at all

1. [(5 * 4 + 5 * 3 + 4 * 3) * 2] * 3-4 * (3 * 4) = 234 (cm2)
2. 80 * 80 * 4 = 25600 (square centimeter)
3. Two sides: (10-2) * 12 = 96
One side: (10 * 10-9 * 4) * 6 = 384
4. (40 / 2 * 6 + 40) / 2 = 80 (cm2)

Xiao Ming's original plan was to take 5 hours and 30 minutes from home to the county town by bike. Because there was a 3-5 / 3 kilometer uneven road on the way, the speed was very slow
How many kilometers is Xiaoming's home away from the county?
Don't answer incompletely. If it's an equation, it's better to list the equation. The process is also better

5 hours 30 minutes = 5.5 hours. Later, 5 hours 42 minutes is 5.7 hours
For 3 and 3 / 5 kilometers on the way, the speed is 3 / 4 of the original speed, so the ratio of the distance to the distance at the original speed is 3:4
That is, one and a half kilometers less
Let the original speed be x km
5.5x = 5.7x-1 and 1 / 5
X=8
Distance from home to the county: 8 × 5.5 = 44 (km)

Calculation problems (life mathematics)
5% of a and 75% of B are equal. Find the simplest integer ratio of a and B

Let a be x and B be y
5/6*X=0.75Y
So x / y = 9 / 10

Use two 12.56 decimeter long wires, one to form a square and the other to form a circle. What is the ratio of the square area to the circle area?

Side length of square = 12.56 △ 4 = 3.14 decimeters
Square area = 3.14 × 3.14 = 9.8596 square decimeters
Radius of circle = 12.56 △ 3.14 △ 2 = 2 decimeters
The area of the circle is 3.14 × 2 & # 178; = 12.56 square decimeters
Square area: circle area = 9.8596:12.56 = 157:200

Given that a and B are rational numbers and a + 3B + (2a-b) √ 3 = 3 + 6 √ 3, try to find the value of a and B

a+3b-3+(2a-b-6)√3=0
A + 3b-3 and 2a-b-6 are rational numbers
3 is irrational
If 0 on the right is irrational, only the coefficient of √ 3 is 0
therefore
2a-b-6=0
So a + 3b-3 = 0
So a = 3, B = 0

1.-5-（-4）+（-3）-2
2. The fourth power of - 2 + / 3-4 / × (- 3) the second power of - 2 * (- 1) the ninety ninth power
3. (- 4 and 1 / 2) △ 41 / 2 × 123 × (- 2 / 9)
4. The fourth power of [3 and 1 / 3 △ (- 2 / 3) × 1 / 5] - the second power of - 2 × (- 3) - (- 5)

1.-5+4-3-2
=-1-3-2
=-6
2. The original formula = - 16 + 1 * 9 + 2
=-5
3. Original formula = - 9 / 2 * 2 / 41 * 123 * (- 2 / 9)
= 6
4. The original formula = - 1 * 1 / 4 + 6 + 5 = - 1 / 4 + 11 = 10 and 3 / 4

It is known that if the side length of a square is increased by 3cm, its area will be increased by 39cm. To find the side length of the square, we can use the complete square formula

Let the original side length be X
（x+3）^2-x^2=39
(x+3+x)(x+3-x)=39
3(2x+3)=39
2x+3=13
2x=10
x=5

When a hollow copper ball with a mass of 89g is suspended in water, the volume of the hollow part of the copper ball is? And the density of copper is 8.9 × 10 cubic kg / M & sup3;