For an activity, I had to record the height of each bounce of a ball. In total I had to do this with 3 balls. Apparently the values are supposed to form a geometric series, but they do not share a common difference as far as I can tell. Here are the values for each of the 3 balls:
Ball 1: 7, 3, 2.5, 1, 0.5
Ball 2: 7, 2, 0.17, 0.04
Ball 3: 7, 3.5, 1, 0.5, 0.17

Can anyone please explain why I'm not finding a common ratio? Am I going crazy or is this activity bogus and the series aren't geometric series?

Question

For an activity, I had to record the height of each bounce of a ball. In total I had to do this with 3 balls. Apparently the values are supposed to form a geometric series, but they do not share a common difference as far as I can tell. Here are the values for each of the 3 balls:
Ball 1: 7, 3, 2.5, 1, 0.5 
Ball 2: 7, 2, 0.17, 0.04
Ball 3: 7, 3.5, 1, 0.5, 0.17

Can anyone please explain why I'm not finding a common ratio? Am I going crazy or is this activity bogus and the series aren't geometric series?