#### Answer

The sequence is not geometric.

#### Work Step by Step

You are given the sequence 20,15,10,5. The starting value is$a_{1}$=20. Find the common ratio by using the formula: R=$\frac{a2}{a1}$,R=$\frac{a4}{a3}$.Plug in the values to get the ratio:
r=$\frac{15}{20}$=$\frac{3}{4}$
r=$\frac{5}{10}$=$\frac{1}{2}$
There is no common ratio. So the sequence is not geometric.