open ended (high) D10 I'd say about 6.1 (which is roughly about 5.5 +5.5/10 )
if it's open ended (low) it changes a little bit, though ...
I'm not sure I understood the first question. You stated the system, but not the event you want to know the probability of :confused:
Not that I can actually answer it, my statistics are way too much rusted at this point

Chacal