Pine planks loaded into a carriage have a mass of 3 tons. The size of one plank is 400x20X2.5 cm.

Pine planks loaded into a carriage have a mass of 3 tons. The size of one plank is 400x20X2.5 cm. How many planks are there in a carriage?

m = 3 t = 3000 kg.
a = 400 cm = 4 m.
b = 20 cm = 0.2 m.
c = 2.5 cm = 0.025 m.
ρ = 500 kg / m3.
n -?
In order to find the number of boards in a carriage n, it is necessary to divide the entire mass m by the mass of one board m1: n = m / m1.
We express the mass of one board m1 by the formula: m1 = ρ * V1, where ρ is the density of the pine, V1 is the volume of one board.
Since the board has the shape of a rectangular parallelepiped, we will find its volume V1 by the formula: V1 = a * b * c.
n = m / ρ * a * b * c.
n = 3000 kg / 500 kg / m3 * 4 m * 0.2 m * 0.025 m = 300.
Answer: there are n = 300 pine boards in the car.