Question

How many ounces of a 35 %35% alcohol solution must be mixed with 1515 ounces of a 40 %40% alcohol solution to make a 38 %38% alcohol​ solution?

Answer 1

Let
`x` be the amount of the 35% solution that will be added. The resulting solution will have a total volume of
`15+x`, 38% of which is alcohol. 40% of 15 is 6, so the 40% solution contributes 6 oz of alcohol. So

`0.35x+6=0.38(15+x)\implies x=10`

oz of the 35% solution need to be added.