Scientific notation is used to write really large numbers, or really small numbers using less digits. For example:
1. Earth's distance from the sun 150,000,000 kilometers. We can rewrite this in scientific notation as 1.5 x

2. The length of a skin cell is 0.00003 meters. We can rewrite this in scientific notation as 3.0 x

3. The world population is about 7,000,000,000. We can rewrite this in scientific notation as 7 x
