Question: Spell-checking Spell-checking software catches "nonword errors," which result in a string of letters that is not a word, as when "the" is typed as "teh." When undergraduates are asked to write a 250-word essay (without spell-checking), the number X of nonword errors has the following distribution:
(a) Write the event "at least one nonword error" in terms of X. What is the probability of this event?
(b) Describe the event X ≤ 2 in words. What is its probability?