Translation:One boss employs seventy thousand employees.
After plural numbers of which the last digit is 0-1 or 5-9 or if it ends with 12-14, the accusative case is transformed into genitive case.
This also applies for the word for thousand. 1000 – tysiąc, 2000 – dwa tysiące, 3000 – trzy tysiące, 4000 – cztery tysiące, but 5000 – pięć tysięcy, 6000 – sześć tysięcy, and so on.
So "tysiąc" behaves like a noun that is in genitive because it is modified by the numeral "siedemdziesiąt", and to say that you are talking about employees, you use the genitive plural of "pracownik", correct? But if it were only seventy of them, you would say "siedemdziesięciu pracowników" because now "siedemdziesiąt" is quantifying the noun directly and that noun is masculine personal? The numbers are hard. :/
This may sound like a simple question, but unfortunately I can't give you a straightforward answer.
There are basically two extremes: 1) The (strict) dictionary definition and 2) people who hardly use them anymore.
The strictest interpretation goes as follows:
Collective numerals are used with a) non-adult animals and people of neuter grammatical gender b) plurale tantum c) groups of mixed sex d) a few fixed idioms.
It is important to note that collective numerals are slowly losing ground to regular numerals. It's a well-known fact among linguists that older, less regular forms are 'kept alive' longer if they are uttered more frequently. A good analogy are the irregular (strong) verbs in English. There are only a couple dozen of them, but if you make a list of the 30 most common verbs in the English language, almost all of them will be irregular. Many of the much less frequently used English verbs used to be irregular in the past, but are now regular, because irregularities are very difficult to maintain, unless you repeat them very often and your brain gets used to them.
The same goes for collective numerals. They are kind of an 'irregularity' if you will, especially because they have a separate inflection paradigm. If we apply the aforementioned concept we get these two rules of thumb:
- The less common the noun, the lower the probability that it will be used with a collective numeral.
- The higher the number (because higher numbers are less common) the lower the probability that it will be used with a collective numeral.
So, we can assume that dwadzieścioro kociąt (twenty kittens) will lose to dwadzieścia kociąt but pięcioro dzieci (five kids) will win by a huge margin against pięć dzieci.
Even though most cases are quite obvious to us, there is still a big grey area. And I have to admit that I often need to check a noun-number combination in the corpus and decide based on usage frequencies whether the collective number is a) mandatory b) highly recommended or c) only an alternative.
There is another problem with "groups of mixed sex" in the aforementioned definition. If you are telling a story about, say, three students and choose trzej studenci instead of troje studentów, it is possible that no one will actually be able to check whether there is a woman among the students or they are all male, especially if it's irrelavant to the story. So such a 'mistake' will often go unpunished and is therefore not really considered a mistake anymore.
And one final thought. Collective numerals only extend to 99. So, if you were talking about needing 292 kittens, you'd need to combine collective and non-collective numerals: "Potrzebuję dwustu dziewięćdziesięciorga dwojga kociąt". Which demonstrates why most people would rather not use them in this case. And that's totally fine.
Oh, I think I still owe you an example for 'mandatory'. If I (a male) were talking to a woman and were telling her that we are both the same age, I'd see no alternative to "Oboje jesteśmy w tym samym wieku", unless of course I chose to omit 'oboje', which would obviously not change the meaning.
Also, I would put almost the entire group "d) fixed idioms" into the mandatory category. It mostly includes some (but not all) body parts and a few historic expressions:
Dwoje oczu, dwoje uszu - Two eyes, two ears.
Rzeczpospolita Obojga Narodów - The Polish-Lithuanian Commonwealth
Dziesięcioro Przykazań - The Ten Commandments.
I'm trying to think of a rule, and I believe that there's no separate 'masculine-personal' form of numerals such as thousand, million, billion etc. - and their multiples.
So for "70 employees" it's indeed "siedemdziesięciu pracowników", but "70 000 employees" is "siedemdziesiąt tysięcy pracowników". And then "70 070" is "siedemdziesiąt tysięcy siedemdziesięciu pracowników".