Christian made a list of five different kinds of brownies: chocolate chip brownies, Rocky Road brownies, brownies with walnuts, peanut butter swirl brownies, and butterscotch brownies. He asked seventy-eight students to choose their favorite brownie from the last. 8/39 of the students liked peanut butter swirl brownies the best. Three-thirteenths of the students preferred Rocky Road brownies. Chocolate chip brownies were the favorite of two-thirteenths of the students. 7/39 of the students just loved brownies with walnuts and the rest of the students liked butterscotch brownies best. How many students preferred butterscotch brownies?
Convert each fraction so that they all have a common denominator
peanut butter 8 / 39 = 16 / 78
rocky road 3 / 13 = 9 / 78
chocolate chip 2 / 13 = 6 / 78
brownies 7 / 39 = 14 / 78
total fraction of students who did not prefer butterscotch 45 / 78 => 45 students
total number of students who did prefer butterscotch 78 – 45 = 33 students
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