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An alloy of copper and tin weights 400 grams. It contains 75% of copper. How much percentage of copper with respect to the initial mixture should be added to the alloy so that percentage of copper increased to 80%?

An alloy of copper and tin weights 400 grams. It contains 75% of copper. How much percentage of copper with respect to the initial mixture should be added to the alloy so that percentage of copper increased to 80%? Correct Answer 25%

Given:

Total initial weight of alloy = 400 grams

Initial copper percentage = 75%

Final copper percentage = 80%

Calculation:

Initial quantity of copper = 75% of 400 = 300 grams

Initial quantity of tin = 100 grams

Let the quantity of copper added be x grams

According to the question,

(300 + x)/100 = 80/20 = 4

⇒ 300 + x = 400

⇒ x = 100 grams

So, copper added = 100 grams

∴ Percentage of copper added = 100 × (100/400) = 25%

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