Lesson plan

Subtract fives and tens from a two-digit number within 100 by using a number line model

teaches Common Core State Standards CCSS.Math.Content.2.MD.B.5 http://corestandards.org/Math/Content/2/MD/B/5
teaches Common Core State Standards CCSS.Math.Content.2.MD.B.6 http://corestandards.org/Math/Content/2/MD/B/6
teaches Common Core State Standards CCSS.Math.Practice.MP4 http://corestandards.org/Math/Practice/MP4
teaches Common Core State Standards CCSS.Math.Practice.MP7 http://corestandards.org/Math/Practice/MP7

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Big Ideas: Numbers can be subtracted more efficiently by combining groups of 5 and 10 and by using landmark numbers. When we subtract a 10 from a 2-digit number, the tens place decreases by one ten and the ones place stays the same. In second grade, students learn to see ten ones as also one ten or one group of ten. Solving problems involving 'friendly' numbers or 'landmark' numbers helps students solve problems within 100 efficiently. Students will use what they know about combinations of ten to help them solve problems involving tens and multiples of ten. When solving problems on the number line, students will keep one number whole and add or subtract the other number in parts. This lesson sets the foundation for students to see a number as tens and ones and be able to efficiently add or subtract fives and tens to/from any two-digit number within 100. Vocabulary: subtract, difference, jump back, decrease, change, pattern, multiples, friendly number, landmark number Special Materials: 0-100 number line classroom number line (optional) base ten models for students who may need to build the numbers