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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