From two alloys, one which contains 20% tin, and the other 40% tin, it is necessary to obtain an alloy with a mass of 4 kg

From two alloys, one which contains 20% tin, and the other 40% tin, it is necessary to obtain an alloy with a mass of 4 kg, which would contain 25% tin. How many kilograms of each alloy do you need to take for this?

1. Let x kg be the mass of the first alloy, and y kg – the mass of the second alloy;
2. Let’s compose the equation:
x + y = 4;
y = 4 – x;
3. Determine how many kilograms of pure tin is obtained from each alloy:
x * 20% = 0.2x;
y * 40% = 0.4y = 0.4 * (4 – x) = 1.6 – 0.4x;
4. Determine how much pure tin will be obtained in the end:
4 * 25% = 1 (kg);
5. Let’s compose and solve the equation:
0.2x + 1.6 – 0.4x = 1;
-0.2x = -0.6;
x = 3 (kg);
y = 4 – x = 4 – 3 = 1 (kg);
Answer: 3 kilograms and 1 kilogram.