What amount(in mL) of pure alcohol should be added to 400 mL of a 15% solution to increase its strength to 32%?

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100 mL

200 mL

300 mL

400 mL

answer is A.

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Detailed Solution

Given, 15 % of alcohol solution is 400 mL.
So, for every 100 mL there is 15 mL of alcohol.
So, there is 15

\times

4=60 mL of alcohol in the given solution.
So, we need to add some pure alcohol.
Let the amount of alcohol added be x.
So, the net solution becomes 400+x.

32 % of 400 + x = 60 + x

\frac{32}{100} \times (400 + x) = (60 + x)

32 (400 + x) = 100 (60 + x)

12800 + 32 x = 6000 + 100 x

68 x = 6800

x = 100

So, the amount of alcohol to add is 100mL.
So, option 1 is correct.

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