Question

how can a set of numbers be accurate but not precise

Answer 1

Take a look at this link --> https://goo.gl/wJN7e6

Answer 2

Imagine that you are shooting a bunch of arrows at a target as in the link above. If the center of the pattern of your arrows is at the center of the bulls-eye, you are accurate. It doesn't matter how large a spread you have for your arrows. They could be all over the target, but as long as the center of the pattern of arrows is at the center of the buss-eye, you are accurate.

Precision is a measure of the spread of your arrow pattern. If your arrows are all hitting at nearly the same spot with a small spread, you are precise. It doesn't matter if your tight pattern is close to the center of the bulls-eye or way off at the edge of the target, if the spread of the arrows is tight, you are precise.

Answer 3

buss-eye --> bulls-eye in previous post