Let me refer to an example of the opposite version (“Sú tri štvrte na..”):
Marek Hlavac-Slovak Language Lessons For Beginners PDF - PDFCOFFEE.COM
I flipped through the document above and found an error, so there may be more (something to bear in mind if you're planning on using it to learn Slovak):
Ten náš kolega bola v pondelok poobede taký pracovitý. = That (female) colleague of ours was so hard-working on Monday afternoon.
…should be either…:
Ten náš kolega bol
a v pondelok poobede taký pracovitý
! = That
(male) colleague of ours was so hard-working on Monday afternoon!
…or:
T
á n
aš
a koleg
yňa bol
a v pondelok poobede tak
á pracovit
á! = That (female) colleague of ours was so hard-working on Monday afternoon!
I had also checked who Mr Marek Hlavac could be, and he seems to be a qualified Slovak person, reference here:
Marek Hlavac, MPP, Ph.D. and here
Marek Hlavac
And Marek uses “sú tri štvrte na …”
Mr. Hlaváč was born in Liptovský Mikuláš (Slovakia) and has likely been living abroad since he was 16. Currently, he teaches economics in Italy. Trying to learn standard Slovak from him may be a bit risky as you will be relying on the accuracy and grammatical correctness of whatever information he put in his document(s) which may not be a good idea, in my opinion.
Maybe there are people
* who say things like "sú tri štvrte na" but I assumed that your objective is to learn correct/standard Slovak and that’s what my original post was meant to reflect.
_________
* On reflection, I think I have, indeed, heard some people say "sú tri štvrte na..." but that does not make it grammatically correct. I was not able to find any discussion on this particular topic so other than the fact that only the "je" version is used as an example in
Slovník súčasného slovenského jazyka (
slovnik.juls.savba.sk), or in the book
Slovenčina pre cudzincov (written by six ladies who seem to be experts in the field)(
upjs.sk) and that searching Google for "sú tri štvrte na" returned only a few results, I have no other official publication handy that I could quote here to back up my post above and to prove to you that the "sú" version is grammatically incorrect.