Final answer:
Archimedes concluded that silver is less dense than gold.
Step-by-step explanation:
Archimedes observed that a gold and silver crown displaced more water than a lump of pure gold, even though they both had the same mass. From his observation, Archimedes concluded that silver is less dense than gold. Density plays a crucial role in Archimedes' principle, where objects will float if their average density is less than that of the surrounding fluid. In this case, the silver crown, being less dense, is able to displace more water and experiences a greater buoyant force, causing it to float.