This is an old one my dad told me, though I've also heard it as a CarTalk puzzler before:
Above is a straight row of 4 dots: it is a 4-dot row.
Next, we have a set of 13 dots that creates 5 different 4-dot rows.
Now again create 5 different 4-dot rows, but using only 10 dots. Rows must be straight. Oh, and before you tricksters try giving me a single long string of dots, a 5-dot row does not count as 2 4-dot rows. You can use a dot multiple times, but rows can't overlap.
It's a five-pointed star, where every vertex is a dot.