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. If it does not contain a fractional part then the decimal representation does not require a decimal point. So the decimal for 331 is 331.
It is 331, exactly as in the question.
The number IS in decimal notation!
3.88 is decimal notation.
42.4 as decimal notation = 42.4
It is already in decimal notation as 4.8
0.05 is already in decimal notation.
decimal notation of 335 = 335.0
300 is already in decimal notation.
decimal notation of 3.159 = 3.159
110.333333333
decimal notation of 960000 = 900000 + 60000
537 in decimal notation = 537.0