SOLUTION: One alloy contains 3 times as much copper as silver. Another contains 5 times as much silver as copper. How much of each must be used to make 14kg in which there is twice as much c

It is a standard mixture/alloy problem in a non-standard formulation.


First what I will do is to re-phrase it to the STANDARD formulation.
It is done in three lines:


     First alloy is 25% silver.

     The second alloy is , or % silver.
     The resulting alloy is , or % silver.


Now let "x" be an amount of the first alloy to be mixed, in kilograms,
and let "y" be an amount of the first alloy to be mixed, in kilograms.


Then your equations are 

x + y = 14,                         (1)   (for total amount)
 = .           (2)   (for the silver content)


Simplify the system (1), (2). For it, multiply the both sides of (2) by 12. You will get

 x +   y = 14,                      (1')
3x + 10y = 56.                      (2')

To solve this system, express x = 14-y from (1') and substitute it into (2'). You will get a single equation for "y"

3(14-y) + 10y = 56.

From this point please complete the assignment on your own.