"Actually, 3 days *could* be the correct answer. If ship A starts at the start point, ship B starts 1/3 of the way there, ship C then 2/3rds. When you then start, 3 days later a ship will have crossed every point on the journey within 3 days."

If the question was "how long does it take 3 ships to cover a third of the distance", then yes, but that's not really the question is it? Presumably because the Royal Mail delivers millions of letters per day, then each one takes a tenth of a second to deliver?

Though I'm charitably assuming you're being rogue-ishly tongue-in-cheek.

How long does it take to dig half a hole though?