Understanding the principles of base ten is essential to understanding numbers and operations. Students will build upon their knowledge of place value and be challenged to use it in the context of algebraic operations. Engaging content encourages students to demonstrate the knowledge they've gained from reading. Eye-catching visuals help walk readers through the math problems, while age-appropriate language encourages learning. Submarines have a very interesting history, which readers learn as they practice fluently adding and subtracting within 1000. This volume meets CCSS Math Standard 3.NBT.A.2.