Is 21.5 * 10^3 in scientific notation? explain

No it is not in scientific notation. For it to be in scientific notation, the decimal has to come after the 2. There can only be one number before the decimal.

2.15 * 10^3 = scientific notation

21.5 * 10^3 = not scientific notation

If you want the history behind it, look it up but pretty much it is easier to represent large numbers in scientific notation and the math gods have deemed the standard for scientific notation to be written as only one number before the decimal