Question

Phil is boiling water on the stove. The pot he is using contains 4 gallons of water. If the water is evaporating at a rate of 1 cup per minute, how long will it be before all the water is gone? (Hint: 1 gallon = 16 cups)

Answer 1

If 1 gallon = 16 cups, then 4 gallons = 64 cups. (16 x 4)
So if there are 4 gallons of water, then there are 64 cups. If 1 cup of water evaporates a minute then it will take 64 minutes for all the water to be gone. 

Answer: 64 minutes
OR
Answer: An hour and 4 minutes