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

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

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.

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.
problem_activity: Narrative
The purpose of this warm-up is for students to interpret and connect base-ten diagrams and equations and describe how they work. This will be useful when students choose their own representations and methods for subtraction during center activities. Although students may notice and wonder many things about these representations, connections to how the representations show subtracting tens from tens and ones from ones are the important discussion points. As they compare the representations, students develop their skill with place value and operation language  (MP6).
Launch
Groups of 2
Display the image.
“What do you notice? What do you wonder?”
1 minute: quiet think time
Activity
“Discuss your thinking with your partner.”
1 minute: partner discussion
Share and record responses.
Student Facing
What do you notice? What do you wonder?
[IMG]
\(66 - 28 \)
\(66 = 50 + 16 \)
\(16 - 8 = 8 \)
\(50 - 20 = 30\)
\(30 + 8 = 38\)
\(66 - 28 = 38\)
Student Response
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Activity Synthesis
“Both of these representations show ways to find the value of
\(66 - 28\)
. How are they the same? How are they different?” (Both show taking tens from tens and ones from ones. Both show decomposing a ten. One uses base-ten diagrams and one uses only numbers and equations.)


correct_option_index: 0

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