Question

As a nasal decongestant, doctors sometimes prescribe saline solutions with a concentration between 6% and

20%. In "the old days," pharmacists had to create different mixtures, but only needed to stock these
concentrations, since any percentage in between could be obtained using a mixture. An order comes in for a
15% solution. How many milliliters of the 20% solution must be mixed with 10 mL of the 6% solution to
obtain the desired 15% solution?

Answer 1

18mL of the 20% solution must be mixed with 10 mL of the 6% solution to

obtain the desired 15% solution

Explanation:

Ignore all of the useless information til the last sentence: How many milliliters of the 20% solution must be mixed with 10 mL of the 6% solution to obtain the desired 15% solution?

Our goal is to find out how many mL of 20% solution is needed to mix with 10mL of 6% solution to achive a 15% solution.

An easy and simple way to do it is to create a system of equation:

We add in x mL of 15% solution(Which has x mL of water and 20%*x mL of salt)

The equation: 15%=(20%x+0.6)/(x+10)

After solving it we get x=18

Therefore:

18mL of the 20% solution must be mixed with 10 mL of the 6% solution to

obtain the desired 15% solution

Hope this helps, have a good day!

Ps. If you have any questions, feel free to ask them in the comment section below-I'll be more than happy to answer.