Wrap a rectangular paper box with a ribbon, 7dm long, 5dm wide and 4dm high. The knotted part is 50dm long. How many decimetres is this belt altogether?
50 cm = 5 decimeters
4×4+2×(7+5)
= 16+2× 12
= 16+24
=40 Deutsche Mark
40+5=45 Deutsche Mark
Answer: This ribbon is * * * 45dm long.