It depends on how big the songs are... apple products only hold low quality MP3's anyway so most of them are 2.5 to 6 Mb so That should give you and average of about 4000 songs but if your into rock or metal closer to 2000 but if your into pop then probably 4500 songs :)
A 16GB ipod can hold 3,600 songs
8,000
about 3500 songs but im not sure
About 4000 songs
around 50.
An 16Gb iPad can hold up to 199 app and 1 video and like 580 photo
About 7000000
About 20,000
Depending on the length of the songs around 3500-3800songs.
That depends on the apps. They vary greatly in size.
About 800 - 1000 give or take a few.
3,500 songs, 20 hours of videos.