a jeweler has five rings, each weighing 18, made of an alloy of 10% silver and 90% gold. She decides to malt down the rings and add enough silver to reduce the gold content for 75%. How much silver should she add?

Question

anonymous · Answer

@Isaiah.Feynman can you please help my friend?? thanks

anonymous · Answer

total weight is 5(18) = 90. And 10% are silver.
Let x = amount of silver added, then
0.10(90) + x = 0.25(90+x)

anonymous · Answer

can you explain this a lil more for me @Isaiah.Feynman

anonymous · Answer

okay but the answer is 18 but im getting 22.5

mathstudent55 · Answer

You don't specify the units, but I'll use grams.

The total weight of all 5 rings is 5 * 18 g = 90 g.
In 90 g of alloy, 90% is gold, that means 90% * 90 g = 81 g of gold.
Since you want the alloy now to be 75% gold, solve the percentage problem below:

81 g is 75% of what?

81 g = 75% * x

81 g = 0.75x

x = 108 g

That means the total weight of the rings must now become 108 g.

Since they already weigh 90 grams, 

108 g - 90 g = 18 g

He needs to add 18 grams of silver.

anonymous · Answer

gracias!

mathstudent55 · Answer

de nada