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

After reading the conditions, we can say that we know the perimeter of the rectangle and it is equal to 40 dm. To find the area of a rectangle, if, in addition to the area, we know that its length is 3 times the width, we first of all find the lengths of the sides of the rectangle.

Let’s denote by x dm the width of the rectangle, knowing that the length is 3 times longer, we will write it as 3x dm.

Let’s compose and solve the equation:

P = 2 (a + b) is the perimeter of the rectangle.

2 (x + 3x) = 40;

x + 3x = 40: 2;

4x = 20;

x = 20: 4;

x = 5 in. width and 3 * 5 = 15 in. length.

We are looking for an area:

S = a * b = 5 * 15 = 75 dm2.

Answer: 75 dm2.