You have a 45-gallon jug and a 124-gallon jug. neither of the jugs has any markings (although you do know their capacities). describe a way to measure exactly one gallon of water.

Pour 4  times of 124-gallon into a big jug.
Amount of water = 124 x 4 = 496 gallons

Then use the 45-gallon jug to scoop out the water 11 times.
Amount of water scooped out = 11 x 45 = 455 gallons

Water remaining = 496 - 450 = 1 gallon.