The perimeter of the rectangle is 40dm. Find the area of a rectangle if its length is three times its width.

To complete this task, we must create an equation. Let the width of the rectangle be x cm, then the length is 3x cm. The perimeter of the rectangle is twice the sum of the length and width. Knowing that the perimeter is 40 decimetres, let’s make an equation.

2 * (3x + x) = 40;

We carry out the addition of similar monomials in parentheses.

2 * 4x = 40;

8x = 40;

x = 40/8;

x = 5 cm.

The width is 5 cm and the length is 3 * 5 = 15 cm.

The area of a rectangle is equal to the product of its length and width.

S = 15 * 5 = 75 cm².

Answer: 75 cm².