Algebra is a foundational concept in the study of mathematics, and readers will delight in learning the principles of operations and algebraic thinking in a relatable and engaging way. Topics such as adding and subtracting within 20, using algebraic principles to solve equations and word problems, and understanding the relationship between addition and subtraction will give beginning math students a firm grasp on basic math concepts. A relatable narrator shows readers how old his cousins are in this title, which teaches the reader to understand subtraction as an unknown-addend problem. This volume meets CCSS Math Standard 1.OA.B.4. This book should be paired with Who's Older? (9781477720820) from the Rosen Math Readers Program to provide the alternative point of view on the same topic.