Answer:
No. The sequence is not arithmetic, but rather geometric.
Step-by-step explanation:
Arithmetic Sequence is a sequence that has common difference.
To find a common difference:-
[tex] \displaystyle \large{a_{n + 1} - a_n = d}[/tex]
Thus:-
20-100 = -80
4-20 = -16
Since both are not common, the sequence is not arithmetic.
Geometric Sequence is a sequence that has common ratio.
To find a common ratio:-
[tex] \displaystyle \large{ \frac{a_{n + 1}}{a_n} = r}[/tex]
Thus:-
20/100 = 1/5
4/20 = 1/5
Since both are common, the sequence is geometric.
Let me know if you have any questions!