Find the width of the rectangle if its perimeter is 20 cm and the length is 8 cm.

To solve the problem, we will use the formula for determining the perimeter of a rectangle P = 2 · (a + b), where a, b are the sides of the rectangle. From the condition of the problem, it is known that the perimeter of the rectangle is 20 cm, and the length is 8 cm.We take the width as x, then we write 20 = 2 (8 + x):
20 = 2 (8 + x);
20 = 16 + 2x;
20 – 16 = 2x;
4 = 2x;
x = 2.
Answer: The width of the rectangle is 2 cm.