There are n keys in the bundle, but only one fits the door's lock.
Trying them one after another, until the right one will be found, what is the probability it will happen on the k_th trial?

(In reply to If the key fits ... (spoiler) by Steve Herman)

I've never really understood this kind of problem; however if the keys are tried one after another, then on the kth trial (k-1) keys would already have been eliminated, wouldn't they, leaving (n-(k-1)) keys?

So the probability of success on that attempt would be 1/(n-k+1)), giving a probability of 1 if the key is the last in the bundle to be tested.

Posted by broll on 2014-10-15 08:50:42