Question

A chemist needs to strengten as $15$% alcoholic solution of one of $32$% alcoholic. How much pure alcohol should be added to $800mL$ of $15$% solution?

Answer 1

Alcohol contained by $800mL$ of $15\%$ alcohol solution $=800\times \frac{15}{100}=120mL$

Let $xmL$ of pure alcohol is added to the solution to make it $32\%$ alcohol.

Now,

Total amount of alcohol in the olution $=(x+120)mL$

Total amount of solution $=800+x$

Therefore,

$\frac{x+120}{800+x}\times 100=32$

$100x+12000=32x+25600$

$100x-32x=25600-12000$

$68x=13600$

$\Rightarrow x=\frac{13600}{68}=200$

Hence $200mL$ of pure alcohol should be added.