One alloy of silver with copper contains 20% silver, the other – 30% silver.

One alloy of silver with copper contains 20% silver, the other – 30% silver. How much each of these alloys should be taken to obtain 500 grams of an alloy containing 28% silver.

Let the first alloy need to be taken x g, then it will contain 0.2 x g of silver. The second alloy, accordingly, will need to take 500 – x g and it will contain 0.3 (500 – x) g of silver. The resulting alloy will be 500 * 0.28 = 140 g of silver.

Then you can write the equation

0.2x + 0.3 (500 – x) = 140.

To solve it you need:

– expand brackets

0.2x + 150 – 0.3x = 140;

– bring similar

-0.1x = -10;

– calculate the unknown value

x = 100.

So, you need to take 100 g of the first alloy and 500 – 100 = 400 g of the second.