With 40 gallons on board and a burn rate of 8 gallons per hour, how many hours can you fly before exhausting the fuel?

• A. 2 hours
• B. 4 hours
• C. 5 hours
• D. 6 hours

Answer: (C)

Endurance is found by dividing the fuel on board by the burn rate, since the burn rate tells you how many gallons are used each hour. With 40 gallons available and a burn rate of 8 gallons per hour, you can fly for 40 ÷ 8 = 5 hours before the fuel runs out. In other words, time equals fuel divided by burn rate when the burn rate is in gallons per hour. For this scenario, that yields five hours of endurance. If you tried shorter times, like two hours would require 16 gallons and four hours would require 32 gallons; six hours would require 48 gallons, which you don’t have. The five-hour result fits exactly with the available fuel.