Effective writing is readable — that is ... know the acronym better than the full expression). Use words for numbers above 10 if these numbers come at the beginning of a sentence or heading ...

A decimal is a way of writing a number that is not whole. Decimal numbers are 'in between' numbers. For example, 10.4 is in between the numbers 10 and 11. It is more than 10, but less than 11.