Which sequences are geometric? check all that apply.
10, 7.5, 5.625, 4.21875, …
160, 40, 10, 2.5, …
20, 70, 245, 857.5, …
13, 16.5, 20, 23.5, …
5, 5.5, 6.05, 6.655, …
16, 17.1, 18.2, 19.3, …

Geometric sequence is an array of number with common ratio, r. This means that dividing the second by the first and the third by the second will give the same quotient. All the items are examined and the results reported in numbered form.

1. geometric, r = 3/4
2. geometric, r = 1/4
3. geometric, r = 7/2
4. not geometric
5. geometric, r = 11/10
6. not geometric.

Thus, among the choices only the fourth and the sixth are not geometric.