What is 8 months as a decimal?

A decimal number is a way of representing a number in such a way that the place value of any digit is ten times that of the digit in the place to its right. If it does not contain a fractional part then the decimal representation does not require a decimal point. So the decimal for 8 months – as in the question. If you want it as a decimal fraction of some other quantity then you need to specify that second quantity.