The sides of the rectangle are 20 cm and 18 cm. Find the side of a square that has the same perimeter as the given rectangle.

First you need to find the perimeter of the rectangle:

P = 2 * (a + b), where P is the perimeter of the rectangle, a is the length of the side of the rectangle, in is the width of the side of the rectangle.

P = 2 * (20 + 18) = 2 * 38 = 72 (cm).

According to the condition, it is specified that the perimeter of the rectangle and the perimeter of the square are equal, and it is also known that in order to find the perimeter of the square, it is necessary to multiply the side of the square by 4, because all sides of the square are equal.

a = P: 4, where a is the side of the square, P is the perimeter of the square.

a = 72: 4 = 18 (cm).

Answer: 18 cm.