The Thirty-Pound Disk of Four Metals
A disk weighing 30 pounds and valued at 600 shillings is cast from four metals fused together: gold, silver, brass, and tin. By weight, there is three times as much silver as gold, three times as much brass as silver, and three times as much tin as brass. How much of each metal does the disk contain?
Reveal the answer
Gold: 9 ounces; silver: 2 pounds 3 ounces; brass: 6 pounds 9 ounces; tin: 20 pounds 3 ounces (12 ounces to the pound) — together making the full 30 pounds. It's one of Alcuin of York's Propositiones ad Acuendos Juvenes (c. 800 CE), built on the geometric progression 1:3:9:27.