Translation:There are six large bridges over this river.
This is just how it works when the "ez" or "az" comes directly before one of these postpositions that starts with a consonant. It drops the "z" and "ez" becomes "e", "az" becomes "a". There is no reason for this, that's just how it is.
I like to think about postpositions as suffixes which started a life on their own. Just like the 'z' in ez and az assimmilates when a suffix that's starting with a consonant is added (abban, ennél, and so on), it assimmilates to nothingness when there's a postposition with a consonant following.
Six? Why not seven? Aren't there seven big bridges above the river in Budapest? :P
Bridges in Budapest: Rákóczi, Petőfi, Szabadság, Erzsébet, Lánchíd, Margit, Árpád, Megyeri. These are eight bridges. :)
Only one end of the Megyeri bridge is in Budapest :)
And also you didn't count the northern wailway bridge.
Well, the reason is simple: whenever you have a demonstrative pronoun (ez/az - this/that), its grammatical baggage copies that of the noun it represents. In this case:
Ez a folyó - this river
Ebben a folyóban - in this river (same suffix, but different vowel harmony)
Ezekhez a folyókhoz - to these rivers
Ez előtt a folyó előtt - in front of this river
E fölött a folyó fölött - above this river. If the postposition starts with a consonant, ez is reduced to e and az to a.
The tips and notes are only available in the web version of Duolingo -- which you could in theory access from a phone if you used the browser to access the website rather than the app.
It's a pity that the tips and notes aren't available in the app, because this way, app users are missing out on a lot of valuable background information that the course maintainers have provided. (And most probably don't even know that they're missing stuff! Especially iOS app users who don't even have access to sentence discussions.)
As for the double fölött, the rule seem to be that if you have ez, az, ezek, azok (this, that, these, those) + a(z) NOUN, then if the noun takes a postposition or a case ending, so will the the ez, az, ezek, azok.
For example, ez a folyó "this river" + fölött = e fölött a folyó fölött "over this river".
ez and az drop their -z before a consonant -- it would stay on if the postposition started with a vowel, as in az alatt a fa alatt "under that tree", from az a fa "that tree" + alatt.
An example with cases: azokban a házakban "inside those houses", from azok a házak "those houses" + -ban.
With case endings, the -z or ez and az gets assimilated, so "inside that house" would be abban a házban, where the -z turned into a -b before the -b- of -ben.
I totally agree with you, I had done quite a bit of this course before I accidentally (wanted to say hi to someone I am connected to) stumbled on the web version of Duolingo and found the Tips section. Not what you would expect of something so crucial!
I recently accessing the web version by phone and couldn't find the tips and notes section! Glad, though surprised, that you could Linda. Either way, it is a big miss not having this in the app.
From what I've heard, the current version of the website is sensitive to screen size, and on small screens it will look like the app (including not displaying the tips and notes) -- unfortunately, in my opinion.
If you get the chance, visit the website with a computer or at least a tablet.
Yes, Betsy77, I want to salute and quote RyagonIV 's "grammatical baggage" rule as well, and to thank mizinamo for the amplification of the implications. Nice catch!
Can someone explain to me why these scentences aren't written in a similar word order in English - surely "Above this river there are six big bridges" would make the whole exercise a lot easier, and less unnecessarily cryptic!
The given translation is probably more natural. But there's absolutely no reason to not use your suggestion either. Report where you can.
Just, unfortunately, no one has been working on suggestion in this course for a couple of weeks. I want to strangle them a little. :´)