Pawn shops

At a local pawn shop, a student finds a medallion that the shop owner insists is pure platinum. However, the student suspects that the medallion may actually be silver and thus much less valuable. The student buys the medallion only after the shop owner agrees to refund the price if the medallion is returned within two days. The student, a chemistry student, then takes the medallion to her lab and measures the density as follows ... 

---