• # Elementary Mathematics Grade 2 Unit 9

Subject: Mathematics
Timeline: 11 days
Unit 9 Title: Subtraction

Unit Overview:

This unit will give the opportunity for students to explore subtraction. At the beginning of the unit students will review strategies for subtraction of 2-digit numbers. Students will be introduced to comparison number stories involving temperature, money, and base-10 blocks. Students will use comparison diagrams to help solve number stories.

Unit Objectives:

At the end of this unit, all students must be able to use subtraction within 100 to solve one- and two- step word problems involving situations of taking from and taking apart with unknowns in all positions, e.g., by using drawings and equations with a symbol for the unknown number to represent the problem. Students must also be able to use strategies based on place value, properties of operations, and/or the relationship between addition and subtraction and relate the strategy to a written method. Students must be able to solve word problems involving dollars bills, quarters, dimes, nickels, pennies, and temperature.

Focus Standards:

PA.CCSS.Math.Content.CC.2.2.2.A.2 Use mental strategies to add and subtract within 20. (2.OA.1)
PA.CCSS.Math.Content.CC.2.1.2.B.3 Use place value understanding and properties of operations to add and subtract within 1000. (2.NBT.5, 2.NBT.7, 2.NBT.8, 2.NBT.9)
PA.CCSS.Math.Content.CC.2.4.2.A.3 Solve problems using coins and paper currency with appropriate symbols. (2.MD.8)

Mathematical Practice Standards:

#1  Make sense of problems and persevere in solving them.

Mathematically proficient students start by explaining to themselves the meaning of a problem and looking for entry points to its solution. They analyze givens, constraints, relationships, and goals.  They make conjectures about the form and meaning of the solution and plan a solution pathway rather than simply jumping into a solution attempt. Proficient students check their answers to problems using a different method.  They continually ask themselves, “Does this make sense?” They can understand the approaches of others to solving complex problems and identify correspondences between different approaches.

#4  Model with mathematics.

Mathematically proficient students can apply the mathematics they know to solve problems arising in everyday life, society, and the workplace. In early grades, this might be as simple as writing an addition equation to describe a situation.

#5  Use appropriate tools strategically.

Mathematically proficient students consider the available tools.

#6  Attend to precision.

Mathematically proficient students try to communicate precisely to others.  They try to use clear definitions in discussion with others and in their own reasoning.  They state the meaning of symbols they choose, are careful about specifying units of measure, calculate accurately and efficiently, and express numerical answers with a degrees of precision appropriate for the problem context.

Concepts - Students will know:
• Application of subtraction algorithms.
Competencies -Students will be able to:
• Solve subtraction comparison number stories.
• Develop strategies of counting back, and adjusting and compensating to solve subtraction and word problems.

Assessments:
• Unit 7 Assessment and Exit Slips (Quizzes)
• Daily RSA

Elements of Instruction:

First Grade Common Core State Standards for Number and Operations in Base 10 states that students can subtract multiples of 10 in the range 10 – 90 from multiples of 10 in range 10 – 90 (positive or zero differences), using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.

Differentiation:

Each lesson has differentiation options for each portion of the lesson. Additional differentiation options are listed with directions and student masters in the Teacher’s Guide to Games.

Interdisciplinary Connections:
• Program related literature books and daily math routines.