Water for Schools
Menu

Worksheet Grade 3 Math

Tallow Creek's Settling Pond Fences: A Grade 3 Perimeter Worksheet

Students find the perimeter of the rectangular settling ponds at a fictional water renewal center, find a missing side, and compare two ponds that need equal fence.

Objectives

  1. Students will find the perimeter of a rectangle when both side lengths are given.
  2. Students will find a missing side length of a rectangle when the perimeter is known.
  3. Students will compare two rectangles that have the same perimeter but different shapes.

Vocabulary

Key words: perimeter, rectangle, side length, settling pond

Teacher overview

Tallow Creek Water Renewal Center is a fictional plant that cleans used water in large rectangular ponds. A safety fence runs all the way around the edge of every pond, so the crew has to measure the distance around a pond before ordering fence. The most common grade 3 error here is adding the length and the width one time only, which counts two sides instead of four; items 1 and 4 are written so a student who does that lands exactly halfway to the right answer. Items 3 and 10 also press on the belief that a longer, thinner pond must need more fence than a square one.

Tallow Creek's Settling Pond Fences: A Grade 3 Perimeter Worksheet — Grade 3 Math
Name: ____________________________ Date: ______________

Student Worksheet

Tallow Creek Water Renewal Center cleans used water in ponds shaped like rectangles. A fence goes around the edge of each pond. The perimeter is the distance all the way around a shape. All lengths here are in meters.

  1. Pond A is a rectangle. It is 30 meters long and 20 meters wide. What is the perimeter of Pond A?
  2. Pond B is a square. Each side is 25 meters long. What is the perimeter of Pond B?
  3. Pond A is 30 meters long and 20 meters wide. Pond B is a square with sides of 25 meters. Which pond needs more fence?
  4. Pond C is a rectangle. It is 40 meters long and 15 meters wide. What is the perimeter of Pond C?
  5. Pond D is a rectangle. Its perimeter is 90 meters. It is 30 meters long. How wide is Pond D?
  6. The fence around Pond C is 110 meters long. A gate that is 5 meters wide fills part of that fence. How many meters of fence are left to build?
  7. A sludge bed is a rectangle. It is 12 meters long and 8 meters wide. What is the perimeter of the sludge bed?
  8. Name the two side lengths of a rectangle that is not 12 meters by 8 meters but still has a perimeter of 40 meters.
  9. Pond E is a square. Its perimeter is 64 meters. How long is each side of Pond E?
  10. A worker says that a pond 20 meters by 10 meters needs the same fence as a pond 15 meters by 15 meters. Is the worker right?

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: 100 meters. The four sides are 30, 20, 30, and 20 meters. Add: 30 + 20 + 30 + 20 = 100 meters. A student who writes 50 added only one length and one width.
  2. Answer: 100 meters. A square has four equal sides, so 25 + 25 + 25 + 25 = 100 meters, or 4 × 25 = 100 meters.
  3. Answer: Neither. Both ponds need 100 meters of fence, so the amounts are equal. Pond A is 30 + 20 + 30 + 20 = 100 meters and Pond B is 4 × 25 = 100 meters.
  4. Answer: 110 meters. The four sides are 40, 15, 40, and 15 meters. Add: 40 + 40 = 80 and 15 + 15 = 30, so 80 + 30 = 110 meters.
  5. Answer: 15 meters. The two long sides use 30 + 30 = 60 meters. The two short sides share what is left: 90 − 60 = 30, and 30 ÷ 2 = 15 meters. Check: 30 + 15 + 30 + 15 = 90 meters.
  6. Answer: 105 meters. Subtract the width of the gate from the whole fence: 110 − 5 = 105 meters.
  7. Answer: 40 meters. The four sides are 12, 8, 12, and 8 meters, so 12 + 8 + 12 + 8 = 40 meters.
  8. Answer: Any rectangle whose length and width add to 20 meters, such as 15 meters by 5 meters. Check the example: 15 + 5 + 15 + 5 = 40 meters. Other correct pairs include 18 and 2, 16 and 4, 14 and 6, 13 and 7, and 11 and 9.
  9. Answer: 16 meters. A square has four equal sides, so divide the perimeter by 4: 64 ÷ 4 = 16 meters. Check: 16 + 16 + 16 + 16 = 64 meters.
  10. Answer: Yes. The first pond needs 20 + 10 + 20 + 10 = 60 meters. The second pond needs 15 + 15 + 15 + 15 = 60 meters. The two ponds hold different amounts of water, yet the fence around each one is the same length.

Differentiation

Support

Give students grid paper and let them draw each pond to scale, one square per 5 meters, then trace the outline with a finger while counting the sides aloud. Provide a four-box recording strip labeled "side 1, side 2, side 3, side 4" so no side is left out of the sum. Work items 1 and 2 together as a class before releasing the rest.

Extension

Ask students to find every whole-number rectangle with a perimeter of 40 meters and to record the pairs in an organized list, then describe the pattern they notice in the length-and-width sums. Follow with a question about which of those rectangles would hold the most water if all the ponds were the same depth.

ELL supports

Pre-teach "perimeter," "side length," "gate," and "settling pond" with a labeled drawing of a rectangular pond with a fence around it. Post the sentence frame "The perimeter is ___ meters because ___ + ___ + ___ + ___ = ___." Allow students to answer items 3 and 10 by circling the correct pond on a drawing and writing the two totals.

Extensions

Have students measure a rectangular area on the school grounds, such as a garden bed or a section of blacktop, in whole meters using a trundle wheel or meter stick. Ask them to record the four side lengths, compute the perimeter, and then explain how much fencing the school would need if that space became a pond at Tallow Creek.