Counting hundreds in Polish - "set" from 500

Saw a TV programme yesterday, the character seemed to be speaking aloud as counting money.

When he got to the 500+ , he said "set" after the number, eg siedemset (700)

Why does Polish have endings change from sto/sta etc to set at 500, all the way through to and including 900?

Also, anyone tell me what (phonetically described now) "yoosh" means? It rhymes with "whoosh!", or I could phonetically describe it as "you-shh", and is a word in Polish I can't find because I don't know how to spell it in Polish. It seems to be said on its own - not in a sentence, like a short instruction or exclamation.

It's just their grammar, word and number endings always change.
Już is the word you are looking for.It means already or yet.

Thanks Pam, that was really a fast reply!

I thought it might be that, but Google Translate says juz differently. Anyway, will take your word for it :o)

That's due to historical development of the language. Perhaps comparison of several Slavic languages would be interesting.

Typology of numerals in various languages: grzegorj.private.pl/typpl/typollicz.html

Polish
100 sto
200 dwieście => dwie (feminine) ście
300 trzysta => trzy sta
400 czterysta => cztery sta
500 pięćset => pięć set
600 sześćset => sześć set
700 siedemset => siedem set
800 osiemset => osiem set
900 dziewięćset => dziewięć set

Lower Sorbian - this language is quite close to Polish
100 sto
200 dwěsćě
300 tśista
400 styrista
500 pěśstow
600 šesćstow
700 sedymstow
800 wosymstow
900 źewjeśstow

Upper Sorbian - closer to Czech
100 sto
200 dwě sćě
300 tři sta
400 štyri sta
500 pjeć stow
600 šěsć stow
700 sydom stow
800 wosom stow
900 dźewjeć stow

Czech
100 sto
200 dvě stě
300 tři sta
400 ètyři sta
500 pět set
600 šest set
700 sedm set
800 osm set
900 devět set

Slovak - the most regular
100 sto
200 dvesto
300 tristo
400 štyristo
500 pä»sto
600 šes»sto
700 sedemsto
800 osemsto
900 devä»sto

Thanks for the comparison and info, Boletus

All except Slovak reflect the old dual number in 200. Also found in proverbs: Mądrej głowie dość dwie słowie.
Would you know if the other languages also reflect the dual number in such forms as rękoma, oczyma and uszyma?

You mean Mądrej głowie dość PO słowie?

I beieve po słowie is the modern version. Most Poles nowadays would find dwie słowie (like dwie krowie) strange. I'm sure Boletus can clear this up.

The point is that this proverb with dwie slowie does not make much of a sense.

Yes, it does - if you understand the ancient dual number. Polonius3 is right.
See for example here: portalwiedzy.onet.pl/141070,,,,podwojna_liczba_rzeczownikow,haslo.html

====================
What's below is mostly of historical interest
From: Gramatyka historyczno-porównawcza języka polskiego, by Antoni Małecki

Singular standalone, conjugates as a neutral noun, such as dzieło
1. N: sto
2. G: sta
3. D: stu
4. A: sto
5. I: stem
6. L: ście

Example, zarobiłem na każdym ście 4 złote

Plural standalone
1. N: sta: trzy-sta
2. G: set: pięć-set
3. D: stu
4: A: sta: cztery-sta
5: I: stom
6: L: stach

Example: Zarobiłem na każdych pięciu stach 10 złotych

Standalone dual number
1. N: ście: dwie-ście
2. G: stu: dwu-stu
3. D: stoma
4. A: ście (dwie-ście)
5. I: stu (dwu-stu)
6. L: stu (dwu-stu)

Singular with nouns (masculine personal, masculine impersonal, feminine, neutral)
1. N: sto mężów, sto koni, sto zbroi, sto siodeł
2. G: stu mężów, stu koni, stu zbroi, stu siodeł
3. D: stu mężom, stu koniom, stu zbrojom, stu siodłom
4. A: stu mężów, sto koni, sto zbroi, sto siodeł
5. I: stu mężami, stu końmi, stu zbrojami, stu siodłami
6. L: (o) stu mężach, stu koniach, stu zbrojach, stu siodłach

Plural number with nouns (masculine personal, masculine impersonal, feminine, neutral)
1. N: trzysta mężów, trzysta koni, trzysta zbroi, trzysta siodeł
2. G: trzechset mężów, trzechset koni, trzechset zbroi, trzechset siodłom
3. D: trzemset (or trzechset) mężom, koniom, zbrojom, siodłom
4. A: trzechset mężów, trzysta koni, trzysta zbroi, trzysta siodeł
5. I: trzystu mężami, końmi, zbrojami, siodłami
6. L: (o) trzechset mężach, koniach, zbrojach, siodlach

Dual number with nouns
1. N: dwieście: dwieście mężów, koni, zbroi, siodeł
2. G: dwustu: dwustu mężów, koni zbroi, siodeł
3. D: dwustu: dwustu mężom, koniom, zbrojom, siodłom
4. A: dwieście: dwieście mężów, koni, zbroi, siodeł
5. I: dwustu: dwustu mężami, końmi, zbrojami, siodłami
6. L: dwustu: o dwustu mężach, koniach, zbrojach, siodłach

Note that the Polish sound you describe as "sh" and "shh" is different from the sound in "woosh". I can't post links but if you google "voiceless retroflex sibilant" and "voiceless palato-alveolar sibilant", you should find recordings of the sounds on Wikipedia. The former is the Polish sound, and the latter is English. The recorded Polish sound is not exactly what a Pole would usually produce, but it is very close.

It was supposed to be "whoosh" above. Typo.

I'll just add that there is nothing strange about the fact that the last sound in "już" is voiceless, even though we usually think of "ż" as a letter denoting a voiced sound. That is because of terminal devoicing in Polish. Wikipedia has an article about it too.