Doreen schmidt is a chemist. she needs to prepare 28 ounces of a 12% hydrochloric acid solution. find the amount of 14% soulution and the amount of 7% soulution she should mix to get this soulution.

Now, let's say we'll use "x" oz of the 14% solution, and "y" oz of the 7% solution.

how much hydrochloric acid is there in the "x" oz of 14%?  well, is just 14% of x, or (14/100) * x, or 0.14x.

how much hydrochloric acid is there in the "y" oz of 7%?  well is just 7% of y, or (7/100) * y, or 0.07y, the rest may be water or some other substance.

now, the mixture needed is 28 oz, and is only 12% of hydrochloric acid, since is 12% hydrochloric acid and the rest water or such, how much hydrochloric acid is there in it?   well, is just (12/100) * 28, or 3.36 oz.

 

how many ounces of the 7% solution?  well y = 28 - x.