# A pharmacist wishes to mix a solution that is 4% Minoxidil. She has on hand 60 ml of a 3% solution and wishes to add some 6% solution to obtain the desired 4% solution. How much 6% solution should she add?

##### 1 Answer
Apr 24, 2016

She should add 30ml.

#### Explanation:

We can express concentration as amount of solute/volume of solution or:

$c = \frac{n}{v}$

So the amount of substance $n$ is given by:

$n = c \times v$

In this problem the total amount of "Minoxidil"^("tm") is the same before and after mixing, so we can set up this equation where $V$ is the volume of the 6% solution:

$\left(60 + V\right) 4 = \left(60 \times 3\right) + 6 V$

$\therefore 240 + 4 V = 180 + 6 V$

$\therefore 6 V - 4 V = 240 - 180$

$\therefore 2 V = 60$

$V = \frac{60}{2} = 30 \text{ml}$