Question

How many gallons of 50% grape juice must be added to 16 gallons of 25%

grape juice to result in a mixture that is 40% juice?

Answer 1

24 gallons of 50% grape juice

Explanation:

if you have 1 gallon of 50% grape juice and 1 gallon of 25% grape juice, the resulting combination will be 2 gallons of 75/2% (or 37.5%) grape juice.

I guessed you would need about 1.5 times of the 50 % mixture to make the 25% mixture into 50 %. I checked, 1.5 times 16 is 24, so I calculated what is the average concentration (24*50 + 16*25)/40, and I got 40 so that guess was correct.