Find the volume of a rectangular parallelepiped that is 21 cm long and 3/7 of the length and 30% of the height.

Let’s calculate the value of the parallelepiped’s width, it leaves 3/7 of the length, that is, 3/7 of 21 cm.

21: 7 * 3 = 9 (cm) – width.

The width is 30% of the height (which means we take the height as 100%), let’s make a short record:

30% – 9 cm,

100% – x cm.

We make the proportion:

30/100 = 9 / x;

30x = 9 * 100;

x = 900/30 = 30 (cm) – height.

Let’s calculate the volume of a rectangular parallelepiped: V = a * b * c (V – volume, a – length, b – width, c – height).

V = 21 * 9 * 30 = 5670 cm3.

Answer: the volume of the parallelepiped is 5670 cm3.