A rectangular sheet of card 32 cm long and 18 cm wide is divided into two equal rectangles by a straight cut parallel to its shorter side. The two pieces are then joined edge to edge along their 16 cm sides to form one longer rectangle. By how many cm does the perimeter increase?

The cut gives two pieces of 16 cm by 18 cm. Joined along a 16 cm side they form a rectangle 16 cm by 36 cm, whose perimeter is 2(16 + 36) = 104 cm, against the original 2(32 + 18) = 100 cm — an increase of 4 cm. The trap 0 assumes the perimeter is preserved because the AREA is (576 sq cm either way), but rearranging pieces conserves area, never perimeter; 104 is the new perimeter quoted instead of the increase; 8 doubles the change.