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Missing Number — Adding to 20 is a free printable Grade 1 maths worksheet on the unknown in an addition crossing ten, aligned to Common Core standard 1.OA.D.8. It prints 9 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 1 of 25 · the same problems every time you open this link.

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One paper per pupil

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All 25 sets ask different questions.

Missing Number — Adding to 20

1.OA.D.8

NameDate

Work out each answer.

1.___ + 9 = 15
2.___ + 6 = 14
3.___ + 7 = 13
4.___ + 8 = 16
5.___ + 8 = 14
6.___ + 6 = 15
7.___ + 7 = 14
8.___ + 8 = 15
9.___ + 9 = 17

LessonPrint · 1.OA.D.8 · Set 1 · free to copy for classroom use

Answer key — Missing Number — Adding to 20

Set 1. Prints on its own sheet.

  1. 1.6
  2. 2.8
  3. 3.6
  4. 4.8
  5. 5.6
  6. 6.9
  7. 7.7
  8. 8.7
  9. 9.8

Questions about Missing Number — Adding to 20

What does the Missing Number — Adding to 20 worksheet cover?

It practises the unknown in an addition crossing ten — 9 questions for Grade 1, all on Common Core 1.OA.D.8: Find the missing number in a number sentence. The instruction to pupils is “Work out each answer”, and the answer key follows on the next sheet.

Which Common Core standard does Missing Number — Adding to 20 practise?

CCSS.MATH.CONTENT.1.OA.D.8 — 1.OA.D.8, in the Operations & Algebraic Thinking domain for Grade 1. The published standard reads: “Determine the unknown whole number in an addition or subtraction equation relating three whole numbers.” The worksheet assesses that standard rather than a paraphrase of it.

What age or grade is this worksheet for?

Missing Number — Adding to 20 is written for Grade 1, typically ages 6-7. It is one of the sheets on 1.OA.D.8, so it suits any pupil working at that standard — including older pupils revisiting it and younger ones working ahead.

Does Missing Number — Adding to 20 come with an answer key?

Yes. All 9 answers are generated from the same problems as the questions, so the key cannot drift out of step with the sheet. It starts on a fresh sheet of paper, after the questions, so it is not handed out with the class by accident.

How many different versions of Missing Number — Adding to 20 can I print?

25 — one per pupil, and all 25 ask different questions. Set 1 downloads the whole class as a single PDF. Every version is fixed to its own address, so a sheet printed today holds the same problems when you reopen it next week.

Is Missing Number — Adding to 20 free to print and photocopy?

Yes. Missing Number — Adding to 20, its answer key and its 25 versions are free to print and photocopy for your own class, with no account, no email capture and no subscription at the download step. Please do not resell them or republish them as your own.

Is there a lesson plan to teach 1.OA.D.8?

Yes — “Finding the Missing Number” is a 40-minute Grade 1 plan for 1.OA.D.8, timed section by section, with the misconceptions to expect and an exit ticket. Missing Number — Adding to 20 is the practice that follows it.

More practice for 1.OA.D.8

Find the missing number in a number sentence.

Teaching this next? Finding the Missing Number is the 40-minute plan for it, with the misconceptions to expect.

All Grade 1 worksheets

Last reviewed 2026-09-05. Aligned to 1.OA.D.8 of the Common Core State Standards for mathematics.