"Costumul primului băiat este negru."

Translation: The costume of the first boy is black.

[IndiraSinghRo]

Oh its so hard

[Gzeebzee]

Or Costumul primul băiatului este negru? but not Costumul băiatului primul este negru because that would be the first costume not the first boy. Interesting.

[relox84]

I'm afraid neither of your sentences make sense: when an adjective comes before a noun, the definite article is attached to the adjective and not to the noun:

Costumul primului băiat = The costume of the first boy

Primul costum al băiatului = The first costume of the boy

[Izzie_gal]

Agreed. Now I am confused.

[0rbital]

"The suit of the first boy is black " is the same of corect.????

[Wes708337]

That was accepted for me.

[rockyroo121]

So why not say the first boys suit is black. ? Thats how it woud be asked

[Wes708337]

It would be "The first boy's suit is black." But as you demonstrated, the use of posessive apostrophes is so confusing in English that it looks like they're avoiding it here.