Dude, are you kidding me :P?
I'm kinda over math 101, and mine are consistently correct.
I encourage you to reread my statement, I did write "chance of winning", I know that dice throws are independent, thanks !
If you need the maths, given 47.1, it's 1-(1-0.471)^2*100%.
Same for 7v8, 1-(1-0.274)^2*100%.
The chance of winning the battle with to roll instead of one is definitely 1-(1-p)^2*100%, where p is the probability of winning. If you want more explanation on that, do not hesitate to ask.
The good question however is the "Where does your 47.1/27.4 come from", and the answer is that I computed the probability the other day.
If you want more infos on that, just ask (I basically computed all permutation of 1 to 8 dices, and sum up all the combinations of battle results for each type of combat, and added the possibility to see how bonuses and maluses change that. It's determinist and exact results (in the given precision, which is derived from BigDecimal scale, up to infinity), it's not simulation-based (what I previously did, far easier but less precise and far less efficient)).