Lesson plan

What's That Number?

Practice finding unknown numbers in addition equations using fun and silly word problems.
Need extra help for EL students? Try the What's the Value? pre-lesson.
EL Adjustments
Grade Subject View aligned standards
Need extra help for EL students? Try the What's the Value? pre-lesson.

Students will be able to find an unknown number in an addition word problem.

The adjustment to the whole group lesson is a modification to differentiate for children who are English learners.
EL adjustments
(5 minutes)
  • Write a story problem up on the board. Read it aloud to your students. For example: "There are 20 animals in the tree. There 10 are snakes, and the rest are monkeys. How many monkeys are in the tree?"
  • Write out a corresponding equation to go with the word problem. For the problem above, write out: 10 + ____ = 20.
  • Ask them to turn and talk with a partner to share how they could solve this problem.
(5 minutes)
  • Have a few pairs share their thinking with the class.
  • Using their ideas, solve the problem on the board. Include drawings and an equation to demonstrate how you can double-check your answer in multiple ways.
  • Explain that sometimes in an equation or math problem we know some parts of the equation, but other parts might be missing. We call the missing pieces the unknown numbers.
(10 minutes)
  • Write a second problem on the board. For example: "There are 25 kids in the class. 15 kids have red shoes, and the rest of the kids have blue shoes. How many kids have blue shoes?"
  • Copy out the corresponding equation on the board: 15 + ____ = 25.
  • Pass out paper to each student and have them work in pairs to solve the problem.
  • Invite one or two pairs to share their work with the class.
  • Clarify any teaching points and answer questions as needed.
(15 minutes)
  • Explain that your students will now complete the What’s Missing worksheet to practice finding the unknown number in each equation.
  • As students finish the worksheet, provide them with blank paper and encourage them to create their own story problem and unknown number equation to trade with a partner.
  • Offer support to your students as needed.


  • Provide math manipulatives for students to use when figuring out the unknown numbers.


  • Have students create two or more story problems featuring a missing number for a peer to complete.
  • Pass out the Unknown Numbers worksheet for additional practice.
(5 minutes)
  • Collect student worksheets and assess whether they were able to find the correct unknown numbers in each problem.
  • Assess whether students were able to solve their classmates' problems.
(5 minutes)
  • Share 1–2 problems created by students with the class. Work together as a group to solve each problem.
  • Answer questions as needed.

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