Question 4.103

4.103 Spell-checking software.

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 of nonword errors has the following distribution:

Value of 0 1 2 3 4
Probability 0.1 0.3 0.3 0.2 0.1
  1. Sketch the probability distribution for this random variable.
  2. Write the event “at least one nonword error” in terms of . What is the probability of this event?
  3. Describe the event in words. What is its probability? What is the probability that ?

4.103

(b) (c) “At most, two nonword errors.”