Lesson plan

6. Solve problems with related facts (A)

teaches Common Core State Standards CCSS.Math.Content.1.OA.C.6 http://corestandards.org/Math/Content/1/OA/C/6
teaches Common Core State Standards CCSS.Math.Practice.MP1 http://corestandards.org/Math/Practice/MP1
teaches Common Core State Standards CCSS.Math.Practice.MP2 http://corestandards.org/Math/Practice/MP2
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Lesson objective: Solve addition and subtraction problems where both "parts" are unknown.

This lesson provides an opportunity for students to apply their knowledge and understanding of addition and subtraction to a real-life situation. Students are asked to figure out how many goldfish and clownfish are in a tank when there are 19 fish in all. 

Key Concept students will use: 

  • We can use strategies such as making ten, counting on, decomposing a number leading to a ten, and the relationship between addition and subtraction to add and subtract within 20.

Skills students will use:

  • Understand addition and subtraction are related
  • Apply properties of operations as strategies to add and subtract (Grade 1, Unit 6)
  • Understand subtraction as an unknown-addend problem (Grade 1, Unit 6)

Students engage in Mathematical Practice 4 (reason abstractly and quantitatively) as they solve problems with both parts unknown.

Key vocabulary: 

  • equal
  • part
  • total
  • whole

Special materials needed:

  • Part Part Total Worksheet (optional)
  • counters or cubes (optional)