A rectangular table top measures 150 cm by 80 cm. What is its area in square metres?

The area is $150\times 80=12000$ sq cm. Since 1 m = 100 cm, one square metre holds $100\times 100=10000$ sq cm, so 12000/10000 = 1.2 sq m. It is quicker still to convert first: 1.5 m $x$ 0.8 m = 1.2 sq m. The trap 120 divides by 100 instead of 10000, the classic slip of applying a LENGTH conversion factor to an area; 12000 leaves the answer in square cm; 0.12 divides by 100000.