Our local scrap merchant had to travel to the county recycling plant, 60 miles away.
On the way there he could only manage a steady 12mph, fully laden.
On the way back, he could manage a steady 16mph.
He placed 24 gallons of fuel in the tank ready for the round trip, thinking that this would be enough as the wagon managed to travel 8 miles per gallon. Unfortunately, a piece of metal pierced his fuel pipe at the start of the trip and the wagon started to lose 1 gallon of fuel per hour.
Luckily he only lost fuel when moving and he lost no fuel whilst unloading his scrap metal.
Were 24 gallons enough for the round trip?
The trip was a total of 120 miles, which at 8 miles to the gallon, used 15 gallons.
The outward trip of 60 miles was at 12 mph, which took 5 hours. The return trip was at 16 mph, which took 3.75 hours. Which is a total journey time of 8.75 hours, which meant that 8.75 gallons were lost.
So, 15 gallons were used for the trip, 8.75 gallons were lost, which is a total of 23.75 gallons. So the 24 gallons was enough for the return trip.