For 19 you can get a line of symmetry between each one that is hand to hand (wing to wing) and each one that is nose to nose. Those total 7. In other words, you can make a fold in many places if you take two at a time (or individuals which is what the problem asks).
Why Geometry Is So Hard (and How to Make It Easier)
If you’ve ever felt like Geometry is a completely different subject than the math you’re used to, you’re not alone. For many students, Geometry is the first...