When Mr. Stanley’s gas tank is full, it holds 15 gallons. Mr. Stanley put 12 gallons of gas into the tank, which filled it up. How full was the gas tank before Mr. Stanley put 12 gallons in?
The correct answer and explanation is:
The gas tank was 3 gallons short of being full before Mr. Stanley added 12 gallons. This is because the full capacity of the tank is 15 gallons, and after Mr. Stanley added 12 gallons, the tank became completely full. So, if the full capacity of the tank is 15 gallons and Mr. Stanley added 12 gallons, that means the tank must have already had 3 gallons in it.
To explain this further, let’s break it down with simple math. The full capacity of the tank is 15 gallons. If Mr. Stanley added 12 gallons to the tank and it filled up completely, it means that the amount of gas in the tank before he added the 12 gallons was the difference between the full capacity and the amount he added. This can be calculated as: Amount of gas already in the tank=Full capacity−Amount added\text{Amount of gas already in the tank} = \text{Full capacity} – \text{Amount added} Amount of gas already in the tank=15 gallons−12 gallons\text{Amount of gas already in the tank} = 15 \, \text{gallons} – 12 \, \text{gallons} Amount of gas already in the tank=3 gallons\text{Amount of gas already in the tank} = 3 \, \text{gallons}
Thus, the gas tank was 3 gallons full before Mr. Stanley added the additional 12 gallons.
This type of question helps practice basic subtraction and understanding of how quantities relate to each other. In everyday scenarios, such as refueling a vehicle, it’s useful to know how much space is left in a tank or how much fuel was already in it. This principle can also apply to other situations where an item has a set capacity and you add a certain amount to it.