# Weight of Copper and Tin to Produce an Alloy of 30% Copper and 10% of Tin

Date of Exam:

**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.

B. 17.5 lb copper and 7.5 lb tin

C. 19.5 lb copper and 5.5 lb tin

D. 18.5 lb copper and 6.5 lb tin

**Answer Key**

[ B ]

**Solution**

$20(100) + 100C = 30(100 + C + T)$

$70C - 30T = 1000$ ← equation (1)

$5(100) + 100T = 10(100 + C + T)$

$-10C + 90T = 500$ ← equation (2)

From equations (1) and (2)

$C = 17.5 ~ \text{lbs}$

$T = 7.5 ~ \text{lbs}$

Answer: [ B ]

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