Start from zero — the basic math you need before everything else
Our number system is built around ten, which makes multiplying and dividing by 10 very easy. Multiplying a whole number by 10 shifts every digit one place to the left, which tacks on a zero. Dividing by 10 shifts everything one place right.
Powers of ten follow the pattern 10¹ = 10, 10² = 100, 10³ = 1000, where the exponent counts the zeros. This is place value at work, and it leads to scientific notation, a handy way to write very big or very small numbers (like 3 × 10⁶ for three million).
The metric system runs on tens, so units convert by shifting digits. There are 10 mm in a cm, 100 cm in a metre, 1000 m in a kilometre — each step is another ×10. Going up a unit divides by 10; going down multiplies by 10. The zeros just track the powers of ten.
▶ Powers of Ten