题目

Does solving a math problem give you a headache? Do you feel nervous when you sit a math exam? For most students, math can be tough but scientists have proved that math problems can actually trigger(引起) physical pain. Scientists came to this conclusion with an in-depth experiment, which was published in the Public Library of Science One journal. They began by finding out how much participants fear math. Those involved were asked a series of questions such as how they feel when they receive a math textbook or when they walk into a math lesson. Based on their answers, participants were小刚在商店里买一个练习本和一支铅笔，练习本1.6元1个，铅笔0.5元一支．付给售货员5元，应找回多少元？