SOLUTION: A random box contains tags marked 1; 2; …; n. Two tags are chosen at random with replacement. Find the probability that the numbers on the tags will be consecutive integers.

The space of events is (n x n)-matrix, whose (i,j)-cell contains the pair of indexes (i,j).


The order does matter and the entire matrix is the space, incliding the diagonal.


Each separate cell / (pair) has the probability  .


The favorable outcomes asre the cells located closest to the diagonal (so called one upper-diagonal and one lover diagonal).


The number of favorable outcomes is (n-1) + (n-1) = 2*(n-1).


Therefore, the probability to get two consecutive number randomply is   P = .    ANSWER