Maths problem: fatigue vs critical hits

[lch]

lch said:
The probability that it is X or greater is: (...) (6-b)(1/6)^(a+1)

I just noticed that it is way easier to get the same result in a different way than I did. We already know that each element in a modulo "layer" shares the same probability, and that all the following layers together are cramped into something having the same probability, too. So you just need to count from the current element to the end and sum up.