suppose the amount of 60% zinc alloy was x should be added to 100 pounds of 40% zinc alloy to produce 45%. Thus the total amount of 45% will be:
(x+100) pounds. Thus:
0.6x+0.4(100)=0.45(x+100)
simplifying the above and solving for x will give us:
0.6x+40=0.45x+45
putting like terms together:
0.6x-0.45x=45-40
0.15x=5
hence
x=5/0.15
x=33 1/3 pounds
