Problem A given alloy contains 20% copper and 5% tin. How many pounds of copper and of tin must be melted with 100 lb of the given alloy to produce another alloy analyzing 30% copper and 10% tin? All percentages are by weight.
Answer Key
Solution
$70C - 30T = 1000$ ← equation (1)
Tin $5(100) + 100T = 10(100 + C + T)$
$-10C + 90T = 500$ ← equation (2)
From equations (1) and (2) $C = 17.5 ~ \text{lbs}$
$T = 7.5 ~ \text{lbs}$
Answer: [ B ]
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