The average roll with a "cap" of Y where the kept values are 1, 2, 3, 4, ..., Y is (Y + 1)/2 = Y + 0.5
You roll X dice. For each die there is a (10 - Y)/10 = 100% - Y*10% chance that you treat the value as zero.
Roll five (i.e. X = 5) dice. Cap = 7 (i.e. Y = 7)
Die #1: 70% chance of avg...