Working with Linear Measurement (including Perimeter)

Primary Standards:

MAFS.3.MD.2.4: Generate measurement data by measuring lengths using rulers marked with halves and fourths of an inch. Show the data by making a line plot, where the horizontal scale is marked off in appropriate units— whole numbers, halves, or quarters.

MAFS.3.MD.4.8: Solve real world and mathematical problems involving perimeters of polygons, including finding the perimeter given the side lengths, finding an unknown side length, and exhibiting rectangles with the same perimeter and different areas or with the same area and different perimeters.

Content Knowledge:

In this unit, students extend their understanding of measurement and fractions by measuring objects to the nearest half and fourth of an inch. Students will also revisit line plots from 2nd grade and record data to the half and fourth of an inch.  Seeing both a line plot and a ruler as a number line helps students see the connection between these number concepts and models.

Perimeter is measured in linear units.  In 3rd grade, students explore the concept of perimeter, calculating the perimeter of polygons and solving problems related to perimeter.   Through problem-based investigations and discussions, students develop an understanding of perimeter and the real-world applications for perimeter.  In the next unit, students will investigate the relationship between area and perimeter.

GCG 1 – Learning Goal:  As a mathematician, I will be able to use strategies to fluently multiply by 7 Ongoing Fluency

  • Step 1: Use distributive property to connect x2 and x5 facts to gain fluency with x7 facts (e.g. 7×8 can be thought of as (5×8) + (2×8))
  • Step 2: Decide when to apply the commutative property and other known facts for efficiency (e.g., students have another strategy for 7×4, they may decide to use double doubles strategy instead)

GCG 2 – Learning Goal:  As a mathematician, I will be able to measure to the nearest whole, half, and quarter inch

  • Step 1: Use a ruler to measure objects to the nearest whole and half inch
  • Step 2: Use a ruler to measure objects to the nearest quarter inch; make connections to half and quarter inch equivalences

GCG 3 – Learning Goal:  As a mathematician, I will be able to create line plots on a horizontal scale using wholes, halves, or fourths

  • Step 1: Interpret and plot measurement data on a provided line plot (with whole, half, and quarter inch units)
  • Step 2: Generate measurement data and create a line plot where the horizontal scale is marked off in appropriate units (whole number, halves, or quarters)

GCG 4 – Learning Goal:  As a mathematician, I will be able to calculate and solve problems related to perimeter of polygons

  • Step 1: Define perimeter (as the linear measurement around a polygon) and measure perimeter of rectangles given side lengths
  • Step 2: Solve real-world problems involving perimeters of polygons
  • Step 3: Find the unknown side-length of a shape (especially rectangles) when given the perimeter

GCG 5 – Learning Goal: As a mathematician, I will be able to use the relationship between area and perimeter to solve problems

  • Step 1: Compare and contrast the concepts of perimeter
  • Step 2: Compare rectangles with the same area and different perimeters AND rectangles with the same perimeter and different areas
  • Step 3: Solve a variety of real-world problems involving area and perimeter (using all four operations)
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