A bookseller sells 15 books in January, 16 in February and a certain number of books in March. If the average number of books he sold per month across all three months is 16, how many books did he sell in March? Give me reasons, before answering the question
He sold an average of 16 books per month across all 3 months so he must have sold a total of 3 * 16 = 48 books in those 3 months. He sold 15 + 16 = 31 in January and February. He must have sold 48 - 31 = 17 books in March. So the final answer is 17.