Zinc and copper are in the ratio of 5 : 3 in 400 gm of an alloy. How much of copper (in grams) should be added in the mixture to make the ratio 5 : 4?

In the original 400 gm alloy, the quantity of copper is (3/8) times 400, which is 150 gm, and zinc is 250 gm. Because the zinc amount remains constant, you need the copper to be (4/5) times 250, which equals 200 gm, to achieve the new ratio of 5 to 4. You must add 200 minus 150, which is 50 gm of copper.

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