This book is a part of the ongoing effort by Areteem Institute to inspire students, parents, and teachers to gain a deeper understanding and appreciation of mathematics. There are five chapters; the first two chapters cover the fundamental concepts of number sense, ratios, percentage, and proportions. The last three chapters cover the real-world applications of those concepts, including word problems in categories such as chicken-rabbit, motion, and work-related problems, suitable for upper elementary school and middle school students in grades 6, 7, and 8. The content is organized to emphasize on the proper implementation of the Common Core Mathematics Standard, focusing on conceptual understanding, problem solving, and real world applications. Different problem solving strategies are presented and compared. Some contest (AMC8, MATHCOUNTS, and ZIML Division M) level problems are included to challenge talented middle school students or advanced elementary school students. For information about Areteem Institute, visit http: //www.areteem.org.