Typographic errors in a text are either nonword errors (as when \"the\" is typed
ID: 3063729 • Letter: T
Question
Typographic errors in a text are either nonword errors (as when "the" is typed as "teh") or word errors that result in a real but incorrect word. Spellchecking software will catch nonword errors but not word errors. Suppose human proofreaders catch 66% of nonword errors. You ask a fellow student to proofread an essay in which you have deliberately made 14 nonword errors.
(a) What is the mean number of errors caught? What is the mean number of errors missed? You see that these two means must add to 14, the total number of errors.
caught
missed
(b) What is the standard deviation of the number of errors caught? (Round your answer to four decimal places.)
(c) Suppose that a proofreader catches 90% of nonword errors, so that p = 0.9. What is in this case? What is if p = 0.99? (Round your answers to four decimal places.)
(d) What happens to the standard deviation of a binomial distribution as the probability of a success gets close to 1?
increases towards 1
increases towards 0
decreases towards 0
decreases towards 10
remains constant
caught
=missed
=Explanation / Answer
a)
caught =np =14*0.66 =9.24
missed =14-9.24 =4.76
b) standard deviation =(np(1-p))1/2 =1.7725
c)
0.9 =(np*(1-p)/)1/2 =1.1225
0.99 =0.3723
d) decreases towards 0
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