Ming wants to make 5 gal. of a 6% acid solution by mixing together a 50% acid solution and pure water. How much of each solution must she use?
0.6 gallons of 50% acid + 4.4 gallons of water
Here's how I'd do it:
The target is 5 gallons of 6% acid.
How many gallons of pure acid are contained in 5 gallons of 6% acid? Answer: 0.06 x 5 = 0.3 gallons.
How may gallons of 50% acid contain 0.3 gallons of pure acid? Answer: 0.3 / 0.5 = 0.6 gallons.
Therefore, take 0.6 gallons of 50% acid, and mix together with 4.4 gallons of water to make your final dilution.