How long would a tablet with a 4000mAh battery last

[Deimantas]

How long would a tablet with a 4000mAh, 3.7V battery last if used:
a) for reading text, with the light dimmed as much as possible
b) using wifi - reading web pages, again preferably light dimmed
c) listening to music on the headphones, otherwise idle. should be much longer than on the speaker right?
d) watching a movie

we're talking about a very cheap tablet, namely GOCLEVER i71. I myself am interested in the possibility of using it to listen to music and read some books concerning my studies for as long as possible - 14,8 watt battery really sounds like something I'd want when I can't charge batteries for a long time. Or would the 1Ghz processor quickly gobble up all the energy anyway?

I understand an extensive study may be difficult to stumble upon, so I'm just asking for opinions and approximations from people who possess tablets, and if your battery is not 4000mAh, don't forget to mention that. Thanks!