Question

26. An alloy contains 89% of copper : find how much copper is
to be mixed to a sample of alloy so as to get 44 kgs of a new metal
having 90% copper in it. Ans. 4 kg. (WBCS (Main), 1999)​

Answer 1

4 kg

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Answer 2

Given info : An alloy contains 89% of copper. Some amount of copper is to be mixed to a sample of alloy so as to get 44 kgs of a new metal having 90% copper in it.

To find : the amount of copper is to be mixed in the sample.

solution : let x kg of copper is mixed.

Initially, alloy contains 89 % of copper

Finally, it contains 90% of copper.

Amount of copper in 44kg = 90% of 44kg = 39.6 kg

so, final mass of another substance = 44 - 39.6 = 44kg

So, final amount of other substance = initial amount of substance [ because no change in other substance]

⇒4.4 kg = 11% of alloy

⇒amount of alloy = 4.4 × 100/11 = 40kg

So, amount of copper is to be mixed = 44kg - 40 kg = 4kg

Therefore 4kg of copper is to be mixed to a sample of alloy.