General - Storage Usage help - numbers don't add up

I am confused how the numbers are adding up for my storage. Maybe someone here has some ideas.

I am viewing Settings - General - Usage to find out my storage.

Question 1
It says I have 11.9 GB used. However, I manually added up all the GB and MB for my apps and it comes to 7.6 GB of storage being used (yes I 'showed all apps'). What's up with this? Why is my Ipad showing I'm using more than 4 Gbs that I actually am?

Question 2
I have a 16 GB Ipad 2. The ipad says I have 11.9 GB used, and 1.9 GB available. This gives me a grand total of 13.8 GB. Where did that other 2.2 GB go (to make 16 GB)?

Thanks for you help,
Shawn

That would be the storage that iOS itself uses. Can't remember the exact figure but a brand new iPad has substantially less than 16Gb available.