The sides of the rectangle are 3: 5. Find these sides if the perimeter of the rectangle is 80 cm.

To find the sides of a parallelogram, we will compose and solve an equation. Let’s start by recalling the formula for finding the perimeter of a parallelogram.

Let’s start by analyzing the conditions of the side of the parallelogram are proportional to the numbers 3: 5. And the perimeter of the parallelogram is also known – 80 cm.

We introduce the coefficient k and write down the lengths of the sides of the parallelogram as 3k and 5k.

P = 2 (a + b);

2 (3k + 5k) = 80;

3k + 5k = 80: 2;

k (3 + 5) = 40;

8k = 40;

k = 40: 8;

k = 5.

The sides of the parallelogram are 3 * 5 = 15 cm and 5 * 5 = 25 cm.