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 type 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 = 0.1, 0.2, 0.3, 0.3, 0.1
(a) Is the random variable X discrete or continuous? Why?
(b) Write the event "at least one nonword error" in terms of X. What is the probability of this event?
(c) Describe the event X ≤ 2 in words. What is its probability? What is the probability that X < 2?