Two alloys contain zinc and tin in the ratios $3:2$ and $2:3$ respectively. If 7 kg of the first alloy and 21 kg of the second alloy are mixed, what is the ratio of zinc to tin in the final alloy?
A9:11
B11:9
C7:9
D5:6
Answer & Solution
Correct answer: A. 9:11
In the first alloy, zinc fraction is $3/5$ and tin fraction is $2/5$. So from 7 kg, zinc $=7\times 3/5=4.2$ kg and tin $=7\times 2/5=2.8$ kg. In the second alloy, zinc $=21\times 2/5=8.4$ kg and tin $=21\times 3/5=12.6$ kg. Total zinc $=12.6$ kg and total tin $=15.4$ kg, so the ratio is $12.6:15.4=9:11$.
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