5 x 10⁶
--------------- = 0.0025 ⇒ 2.5 × 10⁻³
20 x 10⁸
In the number 0.0025, move the decimal spot until it lies between the 2 and the 5. By doing so, you create the number 2.5, which is between 1 and 9. Every number written in scientific notation has to be this way. Then, count how many spots you moved the decimal. If you moved the decimal point to the right, then your exponent will be negative. If you moved the decimal point to the left, your exponent will be positive.
