AI Tutor
Have you ever looked closely at a ruler and noticed all the tiny lines packed between the numbers?
Those tiny spaces measure millimetres (extmm ext{mm}), while the numbered marks show centimetres (extcm ext{cm}).
How do we find how many millimetres are in several centimetres?

Centimetres to Millimetres

Because every 1 cm1\text{ cm} holds 10 mm10\text{ mm}, we multiply by 10 to convert centimetres into millimetres.
For example, if an eraser is 4 cm4\text{ cm} long, we find its millimetres by multiplying: 4×10=40 mm4 \times 10 = 40\text{ mm}
What if you measure a small insect in millimetres and want to know its length in centimetres?

Millimetres to Centimetres

To change millimetres back into centimetres, we group every 10 mm10\text{ mm} into one centimetre by dividing by 10.
If a ladybug is 20 mm20\text{ mm} long, divide by 1010 to find its size in centimetres: 20÷10=2 cm20 \div 10 = 2\text{ cm}
A common mistake is mixing up when to multiply and when to divide.