Answer:
1/4
Explanation:
The common ratio in a geometric sequence is the number you multiply to previous term to get the term after.
Dividing by a number is the same as multiplying by that 1/number.
So the common ratio here is 1/4.
This is a geometric sequence since you are able to find all the terms in this sequence by multiplying 1/4 to it's previous term.
Examples:
160(1/4)=40
40(1/4)=10
10(1/4)=10/4=2.5
2.5(1/4)=2.5/4=0.625.