A math problem

I have what should be a simple math calculation but it doesn't want to work. Our safety director wants to know what percentage of trucks have had daily inspections. He wants an overall total so for instance, I have 3 trucks with Total Inspections of 25,  32, and 30 which equals 87. the trucks were driven a total of 90 days (30 each) which "Should" be 97% but Quickbase doesn't see it that way.
We have:
Electronic Inspections + Paper (Manual entered) Inspections = Total Inspections
Days in the last 30 the truck was driven.
Calculation he wants is Total Inspections/Days Driven (both are based on last 30 days)
 I have summary fields for both of these but the division is off. I don't know if it's because the Total Inspections is also a formula field adding the two together (which seems to be the problem) or what exactly the problem is. If I use the calculation on offices that have zero manual entered inspections, the percentage looks to be correct. Unfortunately, we are not 100% electronic, yet. Is there a solution to this issue is the formula field for total inspections going to throw this off indefinitely? Thank you.