Place Value Comparison- Addition and Subtraction Beyond 20
In this unit, students will learn to use their number sense to compare (using symbols >, =, and <.) and order values of two two-digit numbers. They will model, write and solve addition and subtraction equations within 100 including composing new tens when necessary when adding. The students will apply mental math strategies when adding and subtracting multiples of ten.
Essential Outcomes of the Unit
Number and Operations in Base Ten- Understand place value
NBT.3 Compare two two-digit numbers based on meanings of the tens and ones digits, recording the results of comparisons with the symbols >, =, and <.
Number and Operations in Base Ten- Use place value understanding and properties of operations to add and subtract
NBT.4 Add within 100, including • a two-digit number and a one-digit number, • a two-digit number and a multiple of 10. Use concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction. Understand that in adding two-digit numbers, one adds tens and tens, ones and ones, and sometimes it is necessary to compose a ten. Relate the strategy to a written representation and explain the reasoning used.
Other Standards Addressed in the Unit
Number and Operations in Base Ten- Understand place value
NBT.2c Understand the numbers 10, 20, 30, 40, 50, 60, 70, 80, 90 refer to one, two, three, four, five, six, seven, eight, or nine tens (and 0 ones).
Number and Operations in Base Ten- Use place value understanding and properties of operations to add and subtract
NBT.5 Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.
NBT.6 . Subtract multiples of 10 from multiples of 10 in the range 10-90 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 used to a written representation and explain the reasoning
Essential Questions and Big Ideas
How can we compare values of numbers?
- Numbers sense and understanding of place value are used to compare values of numbers.
- The symbols symbols > means more than, = means equal to, and < means less than when comparing two numbers.
How do we add and subtract within 100?
- Concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction can be used to add and subtract within 100.
- Sometimes it is necessary to compose a new ten when adding within 100.
How can we use number sense and understanding of place value to add and subtract using mental math?
- Understanding number pairs that make ten help to add and subtract mentally.
- Understanding place value and being able to count by tens and add ones can be used to add and subtract mentally.
Download the complete Grade 1 Math Unit 3 framework to customize for your own planning.