Spill or spell? Spell-checking software catches “nonword errors” that 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?
What is the probability that X

Value of X: Probability: 0 1 2 3 4 0.1 0.2 0.3 0.3 0.1