Spelling mistakes in the text are either "nonword errors" or "word errors." A nonword error produces the string of letters that is not a word, such as "the" typed as "teh." Word errors produce the wrong word but words which are valid, such as "loose" typed as "lose." Nonword mistakes make up 25% of all errors. A human proofreader will catch 90% of nonword errors as well as 70% of word errors.
What percent of errors will the proofreader catch?