Final answer:
The number 0.8 is not an integer because it contains a decimal part. All other options are integers as they represent whole numbers.
Step-by-step explanation:
The question asks which of the following is not an integer:
- 17
- 51
- 5 over 1
- -9
- 0.8
- 0
Integer numbers are whole numbers and include negative whole numbers, zero, and positive whole numbers. Choices a) 17, b) 51, c) 5 over 1 (which is equal to 5), d) -9, and f) 0 all represent integers. The number in choice e) 0.8 is not an integer because it has a decimal part and is not a whole number.