"Az egyik fiú hajón utazik, a másik repülőgépen."

Translation: One of the boys is traveling by ship, the other by plane.

[GerSzej]

by is better, but "on a" should also be accepted

[wyqtor]

Also, ship = boat for all these sentences. This lesson is a nightmare to complete.

[Martybet]

They have slowly begun to accept "boat" in a few of these sentences now.
I agree with you on the nightmare bit.

[MichaelC.B7]

official answer 'The one boy travels on a boat, the other one on plane.' sounds quite weird

[Opspin]

Why is it fiú and not fiúk I thought it would be "one of the boys" and this seems like "one of the boy"

[H_Karesz]

A literal translation of the English example sentence: A fiúk egyike hajón utazott, a másika pedig repülőn.

There are 2 versions of the English term 'one of the boys' in Hungarian. (1) a fiúk egyike; (2) az egyik fiú. (1)-phrase is a possessive structure, (2)-phrase is an adjective structure.

[Martybet]

Ok, here Hungarian is probably more logical than English. ' I see three cars' In Hungarian the multiple is already in the number 3 as it would be with many cars 'sok autó'