Essay errors Typographical and spelling errors can be either "nonword errors"
or "word errors." A non-word error is not a real word, as when "the" is typed
as "teh." A word error is a real word, but not the right word, as when "lose"
is typed as "loose." When students are asked to write a 250 -word essay
(without spell-checking), the number of nonword errors X has the following
probability distribution:
Value of X: 01 2 34
Probability: 0.1 0.2 0.3 0.3 0.1
\(\mu_{X}=2.1 \qquad \sigma_{X}=1.136\)
The number of word errors \(Y\) has this probability
distribution:
Value of Y: 0 1 23
Probability: 0.4 0.3 0.2 0.1
\(\mu_{\mathrm{Y}}=1.0 \quad \sigma_{\mathrm{Y}}=1.0\)
(a) Find the mean and standard deviation of the difference \(Y-X\) in the number
of errors made by a
randomly selected student. Interpret each value in context.
(b) Challenge: Find the probability that a randomly
selected student makes more word errors than non-word errors.