A metallurgical workshop produces a special bronze alloy by melting copper, tin, and zinc together in the ratio 5:3:2 by weight. In one production run, the workshop prepares 200 kilograms of this bronze alloy for a shipment of decorative fittings.

Separately, the same workshop also prepares a batch of brass, made only of copper and zinc mixed in the ratio 7:3 by weight, weighing 150 kilograms, for a different order of plumbing fixtures.

To create a new experimental alloy for a customer who wants a metal combining properties of both, the workshop melts together the entire 200-kilogram bronze batch and the entire 150-kilogram brass batch into a single combined mixture, which the workshop's engineers have named Duo-Blend. The engineers now need to work out exactly how much of each metal -- copper, tin, and zinc -- ends up in this new combined mixture, since the customer has asked for a precise composition report before the order can be finalised and shipped.