Spell-checking software catches "nonword errors" which result in a string of letters that is not a word, as when "the" is type "teh." When undergraduates are asked to write a 250 word essay (without spell checking), the number X of nonword errors has the following distribution:

Errors (X)	0	1	2	3	4
Probability	0.37	0.25	0.18	0.12

In the table shown above the probability of exactly 4 errors is not given. Using what you know about probability distributions, what is the probability of exactly 4 errors?

What is the probability of at least 1 nonword error?

Find the expected value of this distribution. How many nonword errors can you expect from a typical paper written under the previously mentioned conditions?