Question

an alloy of gold and silver weighs 50gm it contains 80% gold how much gold should be added to the alloy so that percentage of gold is increased to 90?
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Answer 1

5 grams of gold should be added to make it 90%. 80% of 50g is 40. 10% of 50g is 5. If we add both we get 45 which is the 90% of 50 grams. So the final answer is 5 grams.