how likely is a car to fail?

this straight from the world's best mechanical engineer:

R=(1/6,000,000)(M^1.5)+(.5(Y^1.4)) where M is miles and Y is time in
years. This would give you about 3.5 failures in the first three years,
which is about the average (I saw the numbers on this once and was
surprised the average car gets so much warranty work done).