I'm looking for an algorithm to determine the value of a variable that could be impacted by two percentages that may or may not be overlapping.

For instance:

You have a quantity of engines (E).
25% of E will be unusable due to defect1 (D1)
25% of E will be unusable due to defect2 (D2)
Engines affected by D1 could also be engines affected by D2, there's no reliable way to know until they are tested.

How many engines can reliably predicted to be free of either defect?

I'm sure there's an algorithm or statistical model for this, but have been unable to find it.

Since the two are unrelated, the item has a chance to be free of each defect independently of each other.  The odds that it is free of both defects is the chance that it is free of defect A times the chance that it is free of defect B.  In this case, there is a 25% chance of having the defect (in each case), so the chance of being free of each defect is .75 (1 - .25).  So the odds of being free of both defects is .75 * .75, or .5625.  That is, just over 56%.

Mike

Right.

This problem is basically getting a student to understand the old "heads or tails" coin probability example but with a real-world example. No difference.

In stats this is called the 'general multiplication rule.' :

https://www.khanacademy.org/math/ap-statistics/probability-ap/probability-multiplication-rule/a/general-multiplication-rule

Awesome, these answers are in the area of what I was thinking was probable.  I really appreciate the link.

Thanks all.