There are two alloys, one is 1 part silver and 5 parts copper and the other 3 parts silver and 1 part copper are mixed to form 350 pounds of an alloy that is equal in silver and copper content.how many pounds of each should be used?

Lets make x equal the number times you use the 1/5 ratio alloy and y equal the number of times you use the 3/1 ratio alloy.  You can make the equation (x+3y)-(5x+y)=0 and (x+3y)+(5x+y)=350
Then you can make the system of equation of:
-4x+2y=0 (this is y=2x)
 6x+4y=350  
You can make 6x+8x=350 by through substitution and solve of x.
14x=350
x=25 (which means y=50)

that means that the weight of the 1/5 ratio alloy is 150 pounds.
(25+(5x25))=150
the weight of the 3/1 ratio alloy is 200 pounds.
((50x3)+50)=200

I hope this helps.

OK so, "question" 1 and 2 are an example question of the relationship between mass, volume, and density and they work you through the problem and answer it for you so... you should probably probably just read it.