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Find the Missing Side from the Perimeter is a free printable Grade 3 maths worksheet on working backwards from the perimeter, aligned to Common Core standard 3.MD.D.8. It prints 10 questions with an answer key on its own sheet of paper, in 25 versions that each ask different questions, so no two pupils in the class work from the same page. Print it from the browser or download it as a PDF — no account, no email.

Set 24 of 25 · the same problems every time you open this link.

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Set 1 has all 25 in a single PDF. All 25 sets ask different questions.

Find the Missing Side from the Perimeter

3.MD.D.8

NameDate

Work out each answer.

1.A rectangle has perimeter 30 and one side 11. What is the other side?
2.A rectangle has perimeter 40 and one side 8. What is the other side?
3.A rectangle has perimeter 42 and one side 11. What is the other side?
4.A rectangle has perimeter 20 and one side 7. What is the other side?
5.A rectangle has perimeter 34 and one side 8. What is the other side?
6.A rectangle has perimeter 36 and one side 7. What is the other side?
7.A rectangle has perimeter 18 and one side 6. What is the other side?
8.A rectangle has perimeter 46 and one side 12. What is the other side?
9.A rectangle has perimeter 28 and one side 8. What is the other side?
10.A rectangle has perimeter 40 and one side 12. What is the other side?

LessonPrint · 3.MD.D.8 · Set 24 · free to copy for classroom use

Answer key — Find the Missing Side from the Perimeter

Set 24. Prints on its own sheet.

  1. 1.4
  2. 2.12
  3. 3.10
  4. 4.3
  5. 5.9
  6. 6.11
  7. 7.3
  8. 8.11
  9. 9.6
  10. 10.8

Last reviewed 2026-09-05. Aligned to 3.MD.D.8 of the Common Core State Standards for mathematics.