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Monkey Business Adding with an Unknown Number Activity

Monkey Business addition activity with equation cards such as 7 + ? = 10 for students to match to answer cards, plus a worksheet of the same 16 equations written as missing-number problems within 20.
Monkey Business Adding with an Unknown Number Activity preview: Equation cards with a missing addend
Monkey Business Adding with an Unknown Number Activity preview

Look Inside · 9 pages

Monkey Business cover for solving addition problems with an unknown, with directions to cut, match cards and do a worksheet
Read the directions aloud before setting up the matching game
Missing addend equation cards: students find the unknown in 7 + ? = 10, 10 + ? = 20, ? + 4 = 9 and 9 + ? = 18
First set of monkey cards to cut out for the matching center
Unknown addend equation cards: students solve 5 + ? = 11, ? + 4 = 11, 7 + ? = 15 and ? + 9 = 11 to find each missing number
Second set of cards; mixes the unknown in first and second position
Monkey equation cards with a missing addend: students solve ? + 8 = 12, ? + 3 = 13, 10 + ? = 12 and 4 + ? = 15
Third set of cut-apart cards for partner or small-group play
Addition cards with an unknown addend up to 20: students solve 15 + ? = 16, 12 + ? = 15, 16 + ? = 20 and ? + 10 = 19
Fourth card set, with sums in the upper teens and 20
Final missing-number equation cards: students find the unknown in ? + 3 = 7, ? + 8 = 13, ? + 11 = 15 and 7 + ? = 17
Last set of equation cards to complete the 20-card deck
Sun answer cards to cut out, showing 3, 10, 5, 9, 6, 7, 8, 2, 4, 10, 2 and 11 for students to match to the equation cards
Print on cardstock; students pair each sun with an equation
Remaining sun answer cards numbered 1, 3, 4, 9, 4, 5, 4 and 10, which students match to the missing addend in each equation
Completes the answer deck; check that all 20 suns are cut
Missing Number worksheet: students write the unknown addend in 20 equations such as 7 + __ = 10 and __ + 3 = 13
Follow-up practice or exit check after the card match
Grades
Preschool–Pre-K, Grades 1–2, Elementary
File type
PDF
Preparation
Print ready

Updated Oct 13, 2026

Subject
Math, Addition and Subtraction, Addition
Resource types
Activities
Preparation
Print ready

About this resource

What's inside this resource

This activity is perfect for helping your students practice finding the unknown whole number in addition equations up to 20. This is a great way to help your students improve their math skills.

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In the classroom

Teaching tips & learning objectives

Learning objectives

  • Find the unknown addend in addition equations with sums up to 20
  • Write the missing number to complete an addition equation

Skills covered

  • Solving for an unknown — matching each equation card to the number that completes it

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Resource details

Core concepts

Core concepts

  • Addition
  • Unknown addend
  • Missing number
  • Sums to 20

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Categories this resource belongs to

Math Activities Fun Math Activities 1st Grade Activities Elementary Pre-K Activities Preschool Activities

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