Question

how much pure alcohol must be added to 400ml of a 15% solution to make its strength 32%​
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Answer 1

400ml has 15% alcohol i.e 60ml . This means we have 340ml of water or the liquid with which alcohol is mixed 
Let V be the volume of alcohol added to make the strength 32%
then V/340+V = 32/100. solving this we get V as 160ml

so we need to add 160 -60 = 100ml of alcohol 

Answer 2

400ml has 15percentage alcohol that is 60ml. this means we have 340ml of water or the liquid with which alcohol is mixed. let x be the volume of alcohol added to make the strength 32percentage

The x/340+x=32/100. solving this we get x as 160ml

so we need to add 160-60=100ml of alcohol.

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