Question

A metal alloy is a metal made by blending 2 or more types of metal. A jeweler has supplies of two metal alloys. On alloy is 30% gold and the other is 10% gold. How much of each alloy should the jeweler combine to create 4kg of an alloy containing 15% gold?

Answer 1

He should combine 1 kg of 30% alloy and 3 kg of 10% alloy.

Explanation:

Let x = mass of 30% ally.

Let y = mass of 10% alloy.

He needs 4 kg of alloy, so the first equation, dealing with masses, is

x + y = 4

Now we deal with the amount of gold.

He uses x mass of 30% gold alloy. The amount of gold in that mass is 0.3x.

He uses y mass of 10% gold alloy. The amount of gold in that mass is 0.1y.

The total mass of gold is 0.3x + 0.1y. We are told the told the end alloy is 4 kg of 15% gold alloy. That contains 0.15(4) kg = 0.6 kg of gold.

The second equation is

0.3x + 0.1y = 0.6

Now we put together the two equations as a system of equations.

x + y = 4

0.3x + 0.1y = 0.6

Multiply both sides of the second equation by -10.

-3x - y = -6

Add this equation to the first original equation.

x + y = 4

+ -3x - y = -6

---------------------

-2x = -2

x = 1

Now substitute x = 1 in the first original equation and solve for y.

x + y = 4

x + y = 4

y = 3

Answer: He should combine 1 kg of 30% alloy and 3 kg of 10% alloy.