An alloy of brass is composed of 84.6% copper, 5.20% tin, 6.70% lead, and zinc. What is the number of pounds of zinc required to make 520.0 pounds of alloy?

Answer 1

The percentage of zinc in the alloy is the difference between 100% and the sum of the other percentages: 100% - 84.6% - 5.20% - 6.70% = 3.50%.
The weight of the zinc required is 3.50% of 520.0 pounds: 3.50% * 520.0 pounds = 0.035 * 520.0 pounds = 18.2 pounds. Answer: \boxed{18.2}.