options: Mentally add 10 or 100 to a given number 100–900, and mentally subtract 10 or 100 from a given number 100–900.

Explain why addition and subtraction strategies work, using place value and the properties of operations. (Explanations may be supported by drawings or objects.)

Add and subtract within 1000, 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. Understand that in adding or subtracting three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and sometimes it is necessary to compose or decompose tens or hundreds.

Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.

Add up to four two-digit numbers using strategies based on place value and properties of operations.
problem_activity: Narrative
The purpose of this Number Talk is to elicit the ways students look for to use the structure of two-digit numbers to subtract (MP7). These understandings help students develop fluency and will be helpful later in this lesson when students will need to be able to find the difference between the estimate and actual measurement of an object.
Launch
Display one expression.
“Give me a signal when you have an answer and can explain how you got it.”
1 minute: quiet think time
Activity
Record answers and strategy.
Keep expressions and work displayed.
Repeat with each expression.
Student Facing
Find the value of each expression mentally.
\(37 - 20\)
\(37 - 21\)
\(37 - 17\)
\(37 - 16\)
Student Response
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Activity Synthesis
“How could you use
\(37-20\)
to help you with
\(37 - 21\)
?”


correct_option_index: 3