Final answer:
At least 43 grams of copper must be alloyed with 387 grams of pure silver to produce an alloy that is no more than 90% pure silver.
Step-by-step explanation:
To determine the amount of copper needed to alloy with silver, we can set up a proportion:
Amount of Copper / Amount of Silver = Desired Copper-Silver Ratio
In this case, the desired purity of silver is no more than 90%. This means the desired ratio of copper to silver is:
Amount of Copper / 387 g = (100% - 90%) / 90%
Solving for the amount of copper:
Amount of Copper = (100% - 90%) / 90% * 387 g
Simplifying the equation:
Amount of Copper = 0.1 / 0.9 * 387 g
Amount of Copper ≈ 43 g