How do you write nine thousands as a decmal?

Answer 1

You would write it as 9000 - nothing more, nor less.

A decimal number is simply a way of representing a number in such a way that the place value of each digit is ten times that of the digit to its right. A decimal representation does not require a decimal point. Adding zeros after the decimal point is wrong because they imply a degree of accuracy (significant figures) for which there is no justification.