Teacher:You are given a math word problem and you are supposed to apply multiple mathematical operators like addition, subtraction, multiplication or division on the numbers embedded in the text to answer the following question and then only report the final numerical answer.
Teacher: Now, understand the problem? Solve this instance: At the schools book fair Sam bought 13 adventure books and 17 mystery books . If 15 of the books were used , how many new books did he buy ?
Student:
15