The circumference is reduced by 200 cm, which is twice as long as one side of a rectangle (*2). Two rectangles just form a square, which means that the other side of the rectangle is half as long as this, 50 cm. So the square area is100 *100 = 10000 square centimeters =100 square decimeter. The circumference of the original rectangle is: (50+ 100)*2=300 cm =30 decimeters.