• TOC
  • Courses
  • Blog
  • Shop
  • Search
    • Courses
    • Blog
    • Subreddit
    • Discord
    • Log in
    • Sign up
    • ▾3rd grade
      • ▸Addition, subtraction, estimation
        • •Mentally add within 1000
        • •Round to the nearest 10 or 100
        • •Add and subtract within 1000, abstract
      • ▸Multiplication
        • •Multiplication using rectangular arrays and equal groups, concrete and visual
        • •Multiplication as repeated addition
        • •Multiply, abstract
      • ▸Division
        • •Divide using equal groups
        • •Division as repeated subtraction
        • •Divide, abstract
      • ▸Fractions
        • •Equal shares of shapes and unit fractions
        • •Plot fractions on the number line
        • •Relating fractions to 1
        • •Representing whole numbers as fractions
        • •Comparing fractions with like numerators, denominators, or both
      • ▸Relating multiplication and division
        • •Missing number problems, multiplication and division
        • •Relating multiplication to division
        • •Use properties to multiply and divide
        • •Multiply one-digit numbers by multiples of 10
      • ▸Arithmetic patterns and problem solving
        • •Two-step word problems
        • •Arithmetic and geometric sequences
        • •Patterns in addition and multiplication
        • •Intro to the triangular numbers
        • •Intro to the Fibonacci sequence
        • •Intro to Pascal's triangle
      • ▾Geometry
        • •Shape heirarchy
        • •Area of composite rectangles by counting unit squares
        • •Area and units of measure
        • •Area as multiplication
        • •Area, perimeter, and how they're related
      • ▸Time, measurement, and data
        • •Tell and write time, minute increments
        • •Measure and estimate volumes and masses
        • •Scaled bar and picture graphs
        • •Line plots with fractions
     › 3rd grade › Geometry

    Area as multiplication

    Students will learn how to find the area of a rectangle by multiplying. Students will also learn how to find the area of composite rectangles by adding or subtracting the areas of rectangles. Conclude by challenging your students to find the area of this trapezoid:

    Watch these Khan Academy videos:

    • Comparing areas of plots of land
    • Finding missing side when given area
    • Decomposing shapes to find area: grids
    • Area word problem: house size
    • Transitioning from unit squares to area formula
    • Measuring rectangles with different unit squares
    • Area and the distributive property
    • Decomposing shapes to find area: add
    • Decomposing shapes to find area: subtract

    Do these Khan Academy exercises:

    • Compare areas by multiplying
    • Find a missing side length when given area
    • Area of rectangles
    • Area of rectangles with partial arrays
    • Understand decomposing figures to find area
    • Transition from unit squares to area formula
    • Area and the distributive property
    • Decompose figures to find area

    Conclude by leading this investigation:

    Lazy Toad Puzzles (counting, symmetry)
    by MathPickle

    3.MD.C.7: Relate area to the operations of multiplication and addition. Recognize that area is additive. That is, we can decompose shapes, find their isolated areas, then add to find the total area.

    Lessons and practice problems