Thorpe won the pentathalon and the decathalon of ten extraordinary events.
Are the adjectives pentathalon, decathalon and ten?
No. Pentathlon and decathlon are things -- therefore nouns.
The only adjective you correctly identified is "ten." You missed the other adjective. Please think about what Writeacher and I suggested in the last post.
You can always look words up in a dictionary which lists their parts of speech.