The perimeter of a rectangle is 84 cm find its sides if they are 2: 5.

1. If the length and width of the rectangle are 2: 5, then their sum is 2 + 5 = 7 parts. The sum of the length and width is a half-perimeter. Find the semi-perimeter of the rectangle:

Semi-perimeter = 84/2 = 42 cm.

2. Divide the semi-perimeter into 7 parts, we get the length of one part:

42/7 = 6 cm.

3. Find the side of the rectangle in accordance with their parts, if the length of one part is 6 cm:

Length = 5 * 6 = 30 cm.

Width = 2 * 6 = 12 cm.

Answer: The length of the rectangle is 30 cm and the width is 12 cm.