A rectangular sheet of paper is 20 cm long and 14 cm wide. A triangle is cut from it whose base is one whole 20 cm edge and whose apex touches the opposite edge somewhere along its length. What is the area, in square cm, of the paper left after the triangle is removed?

Wherever the apex sits along the far edge, its perpendicular distance from the 20 cm base is the full width, 14 cm, so the triangle always measures $(1/2)\times 20\times 14=140$ sq cm — exactly half the sheet's 280 sq cm. The paper left is therefore 280 - 140 = 140 sq cm. That is why the apex's position cannot matter, and the option saying more information is needed is the trap the figure is designed to invite; 280 forgets to remove the triangle; 70 halves the sheet twice over.