A rectangular carrier for a microchip measures 45 mm by 32 mm. What is its area in square centimetres? (1 cm = 10 mm.)

The area is $45\times 32=1440$ sq mm. One centimetre is 10 mm, so one SQUARE centimetre is $10\times 10=100$ sq mm, giving 1440/100 = 14.4 sq cm. It is quicker to convert first: 4.5 cm $x$ 3.2 cm = 14.4 sq cm. The trap 144 divides by 10, applying the LENGTH factor to an area; 1.44 divides by 1000, borrowing the factor that belongs to cubic units; 1440 leaves the answer in square millimetres.