Some basic questions on winrate probability

Ok I am really trying to understand this probability stuff, so hopefully you guys can help me out. I have questions but I want more than just answers, I want to know HOW you calculate this so I can do it for myself in the future.

First, over the last 90,000 hands I have run at 1.7bb/100(8 tabling, though that doesn't matter). I have a standard deviation of 15.6. I am supposed to put in 40k hands to meet my goal next month. What are the chances I run:

-0bb/100
0-1bb/100
1-2bb/100
2-3bb/100
3-4bb/100
+4bb/100

Now I also had a little over 100,000 hands before this at about 1.5bb/100, but that database is lost. Let's assume my standard deviation was the same, so my total for 200,000 hands is 1.6bb/100. How drastically does this change the answers above?

Thanks for any help in advance

Jonny C