What are the answers?

Question

How many gallons each of

25

​%

alcohol and

10

​%

alcohol should be mixed to obtain

15

gal of

17

​%

​alcohol?

Gallons of	Solution	Percent	​(as a​ decimal)	Gallons of	Pure Alcohol
x		25
​%equals0.25
y	10
​%equals0.1
15

17

​%equals

How many gallons of

25

​%

alcohol should be in the​ mixture?

nothing

gal

Answer 1

Let x = gallons of the 25% solution and (5-x) = gallons of the 10% solution.

Then use a weighted average: { 25x + 10(5-x) }/(x + 5 - x) = 17

Doing the algebra, we find

15x = 35 or x = 7/3 gallons of the 25% solution

5-x = 8/3 gallons of the 10% solution