What is the common ratio of the sequence 80, 20, 5, 5/4 . . ? what are the next three terms of the sequence?

To find the common ratio in a geometric sequence, u divide the second term by  the first term. 20/80 = 1/4 <== common ratio

Terms are found in a geometric sequence by multiplying each number by the common ratio to get to the next number.

start with 80
80 * 1/4 = 80/4 = 20
20 * 1/4 = 20/4 = 5
5 * 1/4 = 5/4
5/4 * 1/4 = 5/16 <===
5/16 * 1/4 = 5/64 <===
5/64 * 1/4 = 5/256 <===