At the local BrainBashers Internet despatch centre, the packing department was getting ready for the weekend.
However, it was late in the day and the final five packages were ready to be labelled.
Unfortunately, Fred dropped the labels to the packages and then had no idea which label belonged to which packet.
What is the probability that Fred managed to correctly label exactly four of the five packages?
If Fred had correctly labelled four packages, the fifth label would belong to the fifth package and all packages would be correctly labelled.
Therefore it is impossible to label exactly four packages.