The other, hinted point was that just as shifting gears is deterministic and so, despite the odds, quite expectable -- so, too could the hair have gotten into the drain as the deterministic and expectable result of someone putting it there, in the last place they would look after THEY DIDN'T FIND ANY EVIDENCE.
Correct. Insert your own probality, your answer will be very low.
or to assume that they can be multiplied to arrive at an overall probability.,
Probality theory.