Consider "halvtreds," the Danish word for 50. A reasonable person might expect it to mean "half-three" based on pattern recognition and the fact that tre is three. But no! It's actually a compressed version of "halvtredsindstyve," meaning "half-third-times-twenty" or (2.5 × 20).

This continues with "tres" (60), "halvfjerds" (70), and "firs" (80)—all using a vigesimal system that, if you studied French, seems reasonable.

Except, well, the Danes don't properly sanitize their inputs. "femoghalvfjerds" (75) translates to "five-and-half-fourth-times-twenty," combining decimal and vigesimal systems with zero regard for foreigners...