The boilers in a boiler installation consume 780 gallons per hour. The fuel oil storage tank is a vertical cylinder 18 feet in diameter and currently contains oil to a depth of 14.5 feet. At the current consumption rate, approximately how many hours will the supply last?

• A. 30.2 Hours
• B. 40.1 Hours
• C. 28.7 Hours
• D. 35.4 Hours

Answer: (D)

You're being tested on turning tank dimensions into a usable volume and then using that volume to find how long supply will last at a given consumption rate. Start with the storage tank as a cylinder. The radius is half the diameter: 9 ft. The cross-sectional area is πr^2 = 81π square feet. Multiply by the oil depth to get the volume: 81π × 14.5 = 1174.5π cubic feet, which is about 3,689.8 cubic feet.

Convert cubic feet to gallons using 1 ft^3 ≈ 7.48052 gallons: 3,689.8 × 7.48052 ≈ 27,600 gallons of oil in the tank at 14.5 ft depth.

At a consumption rate of 780 gallons per hour, the time the supply will last is 27,600 / 780 ≈ 35.4 hours.