Acomputer program contains one error. in order to find the error, we split the program into 6 blocks and test two of them, selected at random. let x be the number of errors in these blocks. compute e(x).

There are ways of selecting two of the six blocks at random. The probability that one of them contains an error is



So has probability mass function



These are the only two cases since there is only one error known to exist in the code; any two blocks of code chosen at random must either contain the error or not.

The expected value of finding an error is then

300b(x) is graphed by the functio