Find the sides of parallelogram ABCD if its perimeter is 54 cm and side AB is 2 times more than BC.

1. In accordance with the condition of the problem:
AB = 2BC.
2.Considering that the sides of the parallelogram opposite each other (opposite) are equal, its perimeter is calculated by the formula:
P = 2BC + 2AB = 54 centimeters.
BC + AB = 27 centimeters.
3. Substitute in this expression 2BC instead of AB:
BC + 2BC = 27 centimeters.
3BC = 27 centimeters.
BC = 9 centimeters.
AB = 2BC = 2 x 9 = 18 centimeters.
Answer: AB = СD = 18 centimeters. BC = AD = 9 centimeters.