Spell-checking software catches "nonword errors," which are strings of letters that are not words, as when "the" is typed as "eth." When undergraduates are asked to write a 250-word essay (without spell-checking), the number X of nonword errors has the following distribution. Value of X 0 1 2 3 4 Probability 0.10 0.27 0.27 0.20 0.16