Question

How much pure alcohal has to be added to $400ml$ of a solution containing $15\%$ alcohal to change the concentration of alcohal in the mixture to $32\%$?

• A. $60ml$
• B. $68ml$
• C. $100ml$
• D. $128ml$

Answer 1

The correct option is C $100ml$

Here i will assume that alcohol present is $15\%$ by volume.

so the alcohol already present in solution is $400\times \frac{15}{100}=60ml$

let the volume of alcohol added be x ml so the final volume of solution becomes $400+x$

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

$(400+x)\times 32=6000+100x$

$12800+32x=6000+100x$

$68x=6800$

$x=100ml$