This is a children’s math book that aims at helping children understand mathematical concepts by organically combining stories fitting the direction of math education presented in elementary school education courses and enhance problem-solving skills through quizzes. Children will be able to naturally improve their mathematical thinking abilities by having fun reading the Math Detective Series to understand mathematical concepts, as well as observation, reasoning ability, and inference capacities. Some may worry that it will be difficult to solve math quizzes no matter how fun the story is. But no worries because there are the Math Detectives friends! ‘Number and operations’ genius Na Yeon-san, ‘shape and measurements’ genius Lee Do-hyung, and ‘observation and reasoning’ genius Joo Ah- young will help. The math quizzes are not simply for bets, but the Math Detective friends will kindly explain how to solve the problems together with pictures. Three volumes were published.