Unit 2.2 Mental Math
Learning Objectives
Students will be able to:
• Understand why addition and subtraction strategies work using place value.
• Understand why addition and subtraction strategies work using the properties of operations.
• Mentally add and subtract 10 or 100 to a given number 100–900.
• Tell and write time from analog and digital clocks to the nearest five minutes, using a.m. and p.m.
Essential Questions ·
*How can you explain how you mentally calculate _____? (e.g., 367 + 100 or 367–100)
*How can you use place value to help you add (or subtract) mentally?
*How can you use 11 + 9 to help you solve
9 + 11 mentally? (commutative property)
*When adding three numbers, how does the order in which you add the numbers affect the total? (associative property)
*Why do addition and subtraction strategies that use place value as a helper work?
*How is telling time from an analog clock the same/different as telling time from a digital clock?
Key Vocabulary
mental math strategy analog digital interval
Common Core State Standards for Mathematical Content
Number and Operations in Base Ten 2.NBT
Use place value understanding and properties of operations to add and subtract.
2.NBT.8 Mentally add 10 or 100 to a given number 100–900, and mentally subtract 10 or 100 from a given number 100–900.
2.NBT.9 Explain why addition and subtraction strategies work, using place value and the properties of operations.
3 Explanations may be supported by drawings or objects.
Measurement and Data 2.MD
Work with time and money.
2.MD.7 Tell and write time from analog and digital clocks to the nearest five minutes, using a.m. and p.m.
Mathematical Practices to Be Integrated
2 Reason abstractly and quantitatively.
· Know and flexibly use the Commutative and Associative Properties of operations.
· Use manipulatives and symbols to represent problems.
· Practice computation mentally, in a contextualized (e.g., with time) manner and a decontextualized (e.g., numbers only) manner.
6 Attend to precision.
· Calculate using precise and efficient strategies.
· Communicate and clarify reasoning to others.
Students will be able to:
• Understand why addition and subtraction strategies work using place value.
• Understand why addition and subtraction strategies work using the properties of operations.
• Mentally add and subtract 10 or 100 to a given number 100–900.
• Tell and write time from analog and digital clocks to the nearest five minutes, using a.m. and p.m.
Essential Questions ·
*How can you explain how you mentally calculate _____? (e.g., 367 + 100 or 367–100)
*How can you use place value to help you add (or subtract) mentally?
*How can you use 11 + 9 to help you solve
9 + 11 mentally? (commutative property)
*When adding three numbers, how does the order in which you add the numbers affect the total? (associative property)
*Why do addition and subtraction strategies that use place value as a helper work?
*How is telling time from an analog clock the same/different as telling time from a digital clock?
Key Vocabulary
mental math strategy analog digital interval
Common Core State Standards for Mathematical Content
Number and Operations in Base Ten 2.NBT
Use place value understanding and properties of operations to add and subtract.
2.NBT.8 Mentally add 10 or 100 to a given number 100–900, and mentally subtract 10 or 100 from a given number 100–900.
2.NBT.9 Explain why addition and subtraction strategies work, using place value and the properties of operations.
3 Explanations may be supported by drawings or objects.
Measurement and Data 2.MD
Work with time and money.
2.MD.7 Tell and write time from analog and digital clocks to the nearest five minutes, using a.m. and p.m.
Mathematical Practices to Be Integrated
2 Reason abstractly and quantitatively.
· Know and flexibly use the Commutative and Associative Properties of operations.
· Use manipulatives and symbols to represent problems.
· Practice computation mentally, in a contextualized (e.g., with time) manner and a decontextualized (e.g., numbers only) manner.
6 Attend to precision.
· Calculate using precise and efficient strategies.
· Communicate and clarify reasoning to others.