An alloy that is 50% silver is mixed with 500 g of a 5% silver alloy. How much of 50% alloy must be used to obtain an alloy that is 20% silver ?

Question

An alloy that is 50% silver is mixed with 500 g  of a 5% silver alloy. How much of 50% alloy must be used to obtain an alloy that is 20% silver ? 

Answer 1

Let x be the unknown quantity of 50% silver.

Look at the silver concentrations...   This will be 0.5x of actual silver,

Added to 5% silver in 500g or 0.05(500)g of actual silver

Totaling to (500+x)g of 20% silver which will have 0.2(500+x)g of silver

 

Your equation is:

 

0.5x + 0.05(500) = 0.2(500+x)

 

Solve for x to find the grams of 50% silver used