Question 937992
The alloy contains 75 lbs copper in 100 lbs of alloy = 75%
So remaining is Zinc = 25 %

You need to reduce the zinc % to 10% by adding copper which contains no zinc


---	percent	----------------	Amount									
Zinc in Alloy	25	----------------			100	lbs						
copper	0	----------------			x	lbs						
Mixture	10	----------------	100	+	x	lbs						
												
25	*	100	+	0	x	=	10	(	100	+	x	)
2500	+	0	x	=	1000	+	10	x				
0	x		-10	x	=	-2500	+	1000				
-10	x	=	-1500									
/	-10											
x	=	150		lbs	copper							
												
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