# The first alloy contains 10% copper. And the second-25% copper. Of these two alloys, a third alloy weighing 30

The first alloy contains 10% copper. And the second-25% copper. Of these two alloys, a third alloy weighing 30 kilograms containing 20% copper is obtained. What amount of each alloy was used?

Let the first alloy have a lot of x kg, and the second – in kg, then

On the one hand, the mass of the alloy

x + y = 30;

On the other hand, the mass of copper

0.1x + 0.25u = 0.2 * 30.

It turned out two equations with two unknowns.

You can solve them by substitution:

1) express from the first equation

y = 30 – x;

2) Substitute to the second

0.1x + 0.25 * (30 – x) = 0.2 * 30;

3) reveal brackets

0.1x + 7.5 – 0.25x = 6;

4) bring similar

0.15x = 1.5;

5) divided by 0.15

x = 10 kg – the mass of the first and

y = 20 kg – second alloys

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