We have 25% solution and a 50% solution of a chemical. How do we mix them to prepare 100 gallons of 40% solution?

Oct 8, 2016

$40$ gallons of 25% solution and $60$ gallons of 50% solution

Explanation:

The easiest way to solve questions relating to such mixtures is depicted in following diagram.

First write original strength as indicated in first row.
Then write desired strength in the center.
Then find the difference, using the cross.
This gives the ratio, in which original items should be mixed to get desired strength.

Here 25% solution and a 50% solution of the chemical should be mixed in the ratio of $2 : 3$

And as we desire $100$ gallons of 40% solution, we should have

$100 \times \frac{2}{5} = 40$ gallons of 25% solution and
$100 \times \frac{3}{5} = 60$ gallons of 50% solution