John has a very inefficient toilet that uses 5 gallons of water per flush and his household flushed 15 times per day. He replaced it with a toilet that uses 80% less water per flush. How much water did John save in June? Let's be accurate as possible.
He used to use 5 * 15 = 75 gallons of water per day. This means he used 75 * 30 = 2250 gallons a month. His new toilet uses 5 * .8 = 4 gallons less water per flush. So, it only uses 5 - 4 = 1 gallon per flush. That means he uses 1 * 15 = 15 gallons per day. All in all, it accounts for a total usage of 15 * 30 = 450 gallons. So, he saved 2250 - 450 = 1800 gallons per month.
The answer: 1800.