Math Mammoth Early Geometry

81 pages
(answers included)

Contents and sample lessons

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Math Mammoth Early Geometry (2026 edition) is a worktext that covers geometry topics for grade 3. It focuses on these three topics: classifying shapes, area, and perimeter.

Note: the earlier version of this book (prior to July 2026) was longer and covered geometry concepts for grades 1-2. In July 2026, that book was split into two: this one and Math Mammoth Shapes.

In the first three lessons of the book, students sort shapes into categories based on their attributes. They are learning, in particular, about quadrilaterals as a category. Students observe attributes such as the number of sides, presence of right angles, and whether the shape has equal sides or not. They learn about rhombuses, rectangles, and squares, and how a square is also a rectangle and a rhombus.

Their work here prepares students to classify quadrilaterals in great detail in grade 5. Students classify figures in grade 4 also, based on angles, and focusing on triangles in particular. (These topics are covered in Math Mammoth Geometry 1.)

Next, we focus on the area of rectangles and shapes composed of rectangular areas. We start the topic with the lesson Getting Started with Area, where students tile shapes with unit squares cut out of paper, thus learning the foundation of how area is measured. From there, the lessons gradually lead to the thought that area of a rectangle can be found by multiplying its side lengths.

Students learn about different units for area (both metric and customary) and get hands-on experience on finding the area of rectangles by measuring the sides in inches or centimeters.

Then the lessons deal with the area of compound (rectilinear) shapes, whose area can be found by decomposing the shape into (non-overlapping) rectangles.

In this context, we also study the distributive property “in disguise”, in the lesson Area of Decomposed Rectangles. A rectangle is divided into two parts, and its area is found in two different ways: either as the area of the entire rectangle, or by adding the areas of the two parts.

From this area model, we can see that a × (b + c) is equal to a × b + a × c.  The expression  a × (b + c)  is the area of the entire rectangle, with side lengths a and (b + c), and this is equal to the sum of the areas of two rectangles, one with sides a and b, and the other with sides a and c. (The images in the lesson make it more clear.)

In the lesson Multiplying by Whole Tens students learn to multiply a single-digit number by a multiple of ten, for example 3 × 40 or 90 × 7. After that, students use this skill to calculate areas of bigger rectangles in the rest of the lessons in the book.

The last major topic in the book is perimeter. Students learn perimeter as the “go-around measure”: the total distance when you go or travel around the shape. Then, several lessons focus on both area and perimeter, to make sure students learn to distinguish between these two concepts. We investigate rectangles that have the same area but different perimeters, and also rectangles that have the same perimeter but different areas.

This book is also suitable for a geometry notebook or journal project. This simply means that for each new TERM in the book, the student explains that term and draws the corresponding figure, using 1-2 blank pages. In the end, the student will have their very own geometry book to keep and show around!

After studying the lessons in this book, students can continue the study of geometry with Math Mammoth Geometry 1.

The PDF version of this book can be filled in on a computer, phone, or tablet, using the annotation tools found in many PDF apps. See more.