The width of the rectangle is 3 times less than the length, and its pyrometer is 80dm. Find the area of a rectangle.

1. Let the width be equal to y, then the length is equal to 3y. Let’s compose the equation of the rectangle perimeter according to the formula P = 2 * (a + b), where P is the perimeter of the rectangle with adjacent sides a and b:
2 * (y + 3y) = 80,
2y + 6y = 80,
8y = 80,
y = 80/8,
y = 10 dm.
2. Find the length of the rectangle:
10 * 3 = 30 dm.
3. Find the area of the rectangle by multiplying its length by width:
Area = 30 * 10 = 300 dm2.
Answer: the area of the rectangle is 300 dm2.