error – Search area in a PDF

Suppose I have a PDF with mean a and standard deviation b defined as below. How would it go, finding the area under the PDF curve from 1 to 8, and then dividing that value by the area from 0 to 8? After that, I want to divide 7 by that number. Here is the code.

Given what I said, I know that the output should be greater than 7, but for some reason, I'm getting 0.16.

a = 1 / 2Erfc[k/Sqrt[2]]* X
k = 0.2
b = -q Log[2, q] - (1 - q) Log[2, 1 - q]
q = a / x
x = 7

north[
x/((CDF[NormalDistribution[a, b], 8]- CDF[NormalDistribution[a, b], one]) /

(CDF[NormalDistribution[a, b], one]- CDF[NormalDistribution[a, b], 0]))
]