Question

There are 70 students in line at campus bookstore to sell back their textbooks after the finals:19 had math books to return, 19 had history books to return, 21 had business books to return, 9 were selling back both history and business books, 5 were selling back history and math books, eight were selling business and math books, and three were selling back all three types of these books. (1) How many student were selling back history and math books, but not business books? (2) How many were selling back exactly two of these three types of books? (3) How many were selling back at most two of these three types of books?

Answer 1

Main Answer:In the given question, we need to find the number of students who are selling back history and math books but not business books, the number of students selling back exactly two of these three types of books and the number of students selling back at most two of these three types of books. We can solve these using a Venn diagram or the Principle of Inclusion-Exclusion.Using Principle of Inclusion-Exclusion, we can find the number of students selling back history and math books but not business books as follows:Number of students returning history books only = 19 - (9 + 5 + 3) = 2Number of students returning math books only = 19 - (9 + 5 + 3) = 2Number of students returning both math and history books but not business books = (9 + 5 + 3) - 19 = -1 (Since this value is not possible, we take it as 0)Therefore, the number of students selling back history and math books but not business books = 2 + 2 - 0 = 4.Answer in more than 100 words:Let A, B, and C be the sets of students returning math, history, and business books, respectively. We can use the information given in the question to create a Venn diagram and fill in the values as follows:From the above Venn diagram, we can find the number of students selling back exactly two of these three types of books as follows:Number of students returning only math books = 8Number of students returning only history books = 2Number of students returning only business books = 12Therefore, the number of students selling back exactly two of these three types of books = 8 + 2 + 12 = 22.To find the number of students selling back at most two of these three types of books, we need to consider all possible combinations of sets A, B, and C as follows:No set: 0 studentsExactly one set: (19-9-5-3)+(19-9-5-3)+(21-9-5-3) = 9+9+4 = 22Exactly two sets: 22 students (calculated above)All three sets: 3 studentsTherefore, the number of students selling back at most two of these three types of books = 0 + 22 + 3 = 25.Conclusion:Therefore, the number of students selling back history and math books but not business books is 4, the number of students selling back exactly two of these three types of books is 22, and the number of students selling back at most two of these three types of books is 25.