To an alloy of copper and aluminum weighing 5 kg, containing 60% copper, some pure aluminum was added.

To an alloy of copper and aluminum weighing 5 kg, containing 60% copper, some pure aluminum was added. After that, another alloy of the same metals containing 50% copper was added to the new alloy. As a result, 9 kg of an alloy containing 40% copper was obtained. How many kilograms of other alloy were added?

Let’s determine the mass of copper, which is contained in 5 kilograms of the first alloy:
5 * 60/100 = 3 kg.

Let’s find how much copper is in the third alloy, whose mass is 9 kg:
9 * 40/100 = 3.6 kg.

Let’s calculate how much copper was added:
3.6 – 3 = 0.6 kg.

Copper was added as a second alloy and the content was 50%. Determine the mass of the second sleeper:
0.6 * 100/50 = 1.2 kg.

Answer: Added 1.2 kilograms of an alloy containing 50% copper