Spelling mistakes in a text are either nonword errors or wor

Spelling mistakes in a text are either “nonword errors” or “word errors.” A nonword error produces a string of letters that is not a word, such as “the” typed as “teh.” Word errors produce the wrong word, such as “loose” typed as “lose.” Nonword errors make up 25% of all errors. A human proofreader will catch 80% of nonword errors and 50% of word errors. What percent of errors will the proofreader catch?

Solution

percent of erros will be

Nonword errors make up 25% of all errors* 0.50 + “word errors.”* 0.50

percent of erros = 0.25*0.50   +   0.75*0.50 = 0.125+0.375 = 0.5 = 50%