Question

An enemy force is known to be hiding in one of twenty possible locations. General Staff orders a search to be made by picking a site at random, inspecting it, then picking the next site to be inspected at random from among the remaining sites and so on. After fifteen sites have been inspected, the search is still unsuccessful. The General Staff begins to believe that the enemy has somehow vanished. Is this belief justified? What if there were two enemy groups?

Answer 1