Apply Your Knowledge $4\mathrm{.}3$: Errors in Thinking

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You attend a college where the majority of students major in business management and accounting. You run into a friend with a group of fellow students. One of the students is strumming a guitar and has a couple books of poetry with him. You assume he is a music or English literature major, but later you find out that he is an accounting major. What error in thinking have you made?