standard_description: Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.
problem_activity: Narrative
The purpose of this activity is for students to add within 1,000 using any strategy that makes sense to them. The expressions in this activity give students a chance to use different strategies, such as adding hundreds to hundreds, tens to tens, and ones to ones, reasoning with numbers close to a hundred, or using a variety of representations. Students who use base-ten blocks or draw number line diagrams choose appropriate tools strategically (MP5).
Engagement: Provide Access by Recruiting Interest.
Leverage choice around perceived challenge. Invite students to select 3 of the 4 expressions to complete. Encourage the completion of the last two expressions, as they will be the focus of the synthesis.
Supports accessibility for: Organization, Attention, Social-emotional skills
Required Materials
Materials to Gather
Base-ten blocks
Launch
Groups of 2
Give students access to base-ten blocks.
“Take a minute to think about how you could find the value of each sum.”
1 minute: quiet think time
Share responses.
Activity
“Work with your partner to add these numbers in any way that makes sense to you. Explain or show your reasoning.”
5-7 minutes: partner work time
Monitor for an expression for which students use a variety of representations, such as:
Using base-ten blocks
Drawing a number line
Writing their reasoning in words
Writing equations
Identify students using different representations to share during synthesis.
Student Facing
Find the value of each sum in any way that makes sense to you. Explain or show your reasoning.
\(325 + 102\)
\(301 + 52\)
\(276 + 118\)
\(298 + 305\)
Student Response
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Activity Synthesis
Select previously identified students to display their work side-by-side for all to see.
“Which representations show the same idea or help us find the sum the same way?” (The base-ten blocks and equations show adding hundreds to hundreds, tens to tens, and ones to ones. The number line and the words both added on the second number to the first number in parts.)


aligns: no