An alloy of copper and tin weighing 1kg consist of 70% copper, how much copper should be added to it so that it would contain 75% copper? What will be the weight of the new alloy? A. 30 B. 200 C. 90 D. 120 Answer Workspace Report Discuss Answer with explanation Answer: Option B Explanation Suppose that x kg copper is to be added to the 1 kg alloy. Now, we know that, the 1 kg alloy has 0.7 kg copper. And, final percentage of copper in alloy is 75%. (0.7+x)/(1+x)=75/100=3/4(0.7+x)/(1+x)=75/100=3/4 On cross-multiplication, 2.8+4x = 3+3x x= 0.2 Therefore, 0.2 kg or 200 g copper should be added to make it’s percentage in the alloy 75%. Workspace
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