This grade 3 perimeter test answer key gives the full solution and the scoring guide for each of the 9 test questions on perimeter.
Worked solutions and a scoring guide for the Grade 3 perimeter test. Each answer shows the sum of the sides or the subtraction for an unknown side, and the scoring note tells how many of the 20 points each step earns.
Grade 3 Perimeter Test Answer Key: questions 1–5
Question 1: Perimeter of a triangle (2 points)
\(8 + 13 + 11 = 32\). The perimeter is 32 cm.
Scoring: 1 point for adding all three sides, 1 point for 32 cm with the correct unit.
Question 2: Rectangle and square (2 points)
(a) \(13 + 8 + 13 + 8 = 42\). The perimeter is 42 feet.
(b) \(4 \times 9 = 36\). The perimeter is 36 feet.
Scoring: 1 point for each correct perimeter with units. An answer that gives 21 (half the perimeter) earns no point.
Question 3: Unknown side length (2 points)
Known sides: \(6 + 5 + 9 = 20\). Unknown side: \(24 – 20 = 4\).
The unknown side is 4 meters. Check: \(6 + 5 + 9 + 4 = 24\).
Scoring: 1 point for adding the known sides (20), 1 point for the unknown side of 4 meters.
Question 4: Missing width (2 points)
Two lengths: \(9 + 9 = 18\). \(28 – 18 = 10\), and \(10 : 2 = 5\).
The width is 5 inches.
Scoring: 1 point for finding that the two widths together are 10 inches, 1 point for a width of 5 inches.
Question 5: Fence sections (2 points)
Perimeter: \(18 + 12 + 18 + 12 = 60\) feet.
\(60 : 10 = 6\). She needs 6 sections.
Scoring: 1 point for the perimeter of 60 feet, 1 point for 6 sections.
Grade 3 Perimeter Test Answer Key: questions 6–9
Question 6: Perimeter of an L-shape (3 points)
The two unlabeled sides: the right side of the top part is \(7 – 3 = 4\) cm, and the horizontal step is \(9 – 4 = 5\) cm.
Add all six sides: \(4 + 4 + 5 + 3 + 9 + 7 = 32\).
The perimeter is 32 cm. (Check: \(2 \times (9 + 7) = 32\).)
Scoring: 1 point for each of the two missing sides (4 cm and 5 cm), 1 point for the total of 32 cm.
Question 7: Same perimeter (2 points)
(a) A: \(9 + 3 + 9 + 3 = 24\). B: \(6 + 6 + 6 + 6 = 24\). Both are 24 cm.
(b) \(9 \times 3 = 27\) and \(6 \times 6 = 36\). Rectangle B has the greater area.
Scoring: 1 point for both perimeters equal to 24 cm, 1 point for naming Rectangle B with the areas 36 and 27 shown.
Question 8: Same area (3 points)
(a) \(8 + 2 + 8 + 2 = 20\) units and \(4 + 4 + 4 + 4 = 16\) units.
(b) \(16 < 20\), so the 4-by-4 square has the shorter perimeter.
Scoring: 1 point for each correct perimeter, 1 point for naming the 4-by-4 square.
Question 9: Ribbon for two cards (2 points)
Rectangle: \(7 + 5 + 7 + 5 = 24\). Square: \(4 \times 8 = 32\).
\(24 + 32 = 56\). She uses 56 inches.
Scoring: 1 point for both perimeters (24 and 32), 1 point for the total of 56 inches.
Scoring summary
20 points: add the points of every question of this grade 3 perimeter test answer key.
How to use this grade 3 perimeter test answer key
Use this grade 3 perimeter test answer key to score the test fairly and to see which skills need more practice.
See every chapter on the Grade 3 math page.