enVision Mathematics Grade 3, Topic 16: Solve Perimeter Problems
In this unit, your child finds perimeter, the distance all the way around a shape, by adding its side lengths. They find a missing side when the perimeter is known and see that shapes with the same perimeter can cover different areas. It closes the year by building on shapes from the last unit and area from earlier in the year.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Topic 16?
- Adding side lengths to find perimeter, working back to a missing side, and comparing rectangles with the same perimeter but different areas. Learn more: Perimeter: the distance around a shape
Sample questions to try together
These are real questions from our practice. Tap the speaker to hear one read aloud, or the light bulb for a hint, and talk about the answer together.
Question 1 of 3
A rectangular garden has sides that are 5 feet long and 3 feet wide. What is the perimeter of the garden?
- 8 feet
- 15 feet
- 16 feet
How you can help
- Walk around the edge of a room or table and count your steps, then talk about how the total is the perimeter in steps.
- Give your child 12 toothpicks and ask how many different rectangles they can make using all of them, then compare the space each covers.
- Measure the sides of a placemat or book cover with a ruler and add them, so a 12-inch by 9-inch book has a perimeter of 42 inches.
Where kids can get stuck
- Multiplying the sides to find perimeter, mixing it up with area, so a 5 by 3 rectangle gets 15 instead of 16.
- Adding only the two side lengths shown, forgetting a rectangle has two more matching sides.
- Assuming equal perimeters mean equal areas, so a 7 by 1 rectangle and a 4 by 4 square seem the same size.
Practice makes perfect
Bobby's Math Club has practice problems that adapt to your child’s level, each with a detailed explanation and an easy-to-follow video, so your child can build confidence in these skills one step at a time.
Words your child will hear
- perimeter
- The total length of all the sides of a shape.
- side length
- How long one side of a shape is.
- polygon
- A flat shape made of straight sides that close up, like a triangle or hexagon.
- unknown
- The number we are trying to find, shown by a box, a question mark, or a letter.
- area
- The space inside a flat shape, measured in squares.
- rectangle
- A quadrilateral with 4 square corners.
Want to help your child master perimeter?
In Bobby's Math Club, your child practices these skills at just the right level, with a hint when they need one, a clear explanation after every question, and kid-friendly videos. Unlimited practice is free.
Join the club
Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.
Which math standards does enVision Mathematics Grade 3 Topic 16 cover?
enVision Mathematics Grade 3 Topic 16 covers this math standard. Each one links to what it means, sample questions, and teaching strategies.
- 3.MD.D.8: Find the perimeter, the distance around a shape, or a missing side.
For teachers: Unit names and order vary between editions and districts, so your school’s own materials have the exact sequence. Learn how Bobby's Math Club can help your students grow.