1. We can see if it is arithmetic or geometric. Obviously it is not arithmetic because 9 - 4 is not 4 - 1, and it is not geometric because 9/4 is not 4/1 = 4. So, the answer is Neither.
2. Let's first see if it is arithmetic. We can see that 20 - 18.5 is 1.5, so it goes down by 1.5. The next term also goes down by 1.5, and so on. So, this is an arithmetic sequence.
3. For this one, we can tell it is not geometric because 10/9 is not 9/8. If it was arithmetic, the positive number would've be negative or vice versa. So, this is Neither.
5. This is not geometric because 10/8 is not 8/5. Also, this is close to being arithmetic, but 10 - 8 is not 8 - 5, so it is neither.