"The sum of three and five is eight."

Translation: Suma trzech i pięciu to osiem.

[Ifrit_I3T]

You can also translate it to "Sumą trzech i pięciu jest osiem".

[Jellei]

Could be. Added.

[RobinB896941]

Więc: suma i sumą są dobrze - ale dlaczego??

[Jellei]

"Suma trzech i pięciu to osiem" vs "Sumą trzech i pięciu jest osiem".

It's our usual "X is Y" sentence, but turned around, to "Y is X" because it seems pretty probable here - in fact, it makes more sense to put "osiem" in the end as this is like a maths equation and therefore "eight" is the 'new information'.

Also: Eight is 'a sum', but it's hard to say that 'the sum' is 'an eight', so you wouldn't put eight in Instrumental.

[conor.raff]

Whats going on here?

Three different number forms are being used in the same sentence, and to me it appears as if they are all being used in the same way??

Is the point of this one to show that all three forms are valid when you are doing maths like this and not referring to nouns?

[mihxal]

"Trzy" and "pięć" are used in Genitive. You can just say: "Trzy plus pięć to/równa się osiem".

[conor.raff]

Ah, I see... it's because "suma" takes the genitive....

When I write it like this in English it makes sense:

"the sum of three (gen.) and of five (gen.) =(/"to") eight (nom.)"

[conor.raff]

..and they used the masc. gen. of trzy = "trzech", instead of the other gen. of trzy = "trzej"

Dzięki za odpowiedż!

[immery]

trzej is nominative. only other genitives of three are trojga (from troje), and trójki (from trójka)
We usually use masculine numerals in maths.

[conor.raff]

Dzięki za pomoc!

[TheAlysse]

Why not "Suma z trzech i pięciu to osiem"?