standard_description: Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases:
- The numbers from 11 to 19 are composed of a ten and one, two, three, four, five, six, seven, eight, or nine ones.
- 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).
- 10 can be thought of as a bundle of ten ones — called a “ten.”
problem_activity: Narrative
The purpose of this Number Talk is to elicit strategies and understandings students have for adding within 100. These understandings help students develop fluency and will be helpful later in this lesson when students add two-digit numbers using methods based on place value.
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.
\(13 + 21\)
\(13 + 31\)
\(23 + 31\)
\(33 + 41\)
Student Response
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Activity Synthesis
“How can
\(23 + 31\)
help you solve
\(33 + 41\)
?” (The tens are changing again. In
\(33 + 41\)
, you are adding 2 tens total, so the sum of
\(23 + 31\)
increases by 20.
\(54 + 20 = 74\)
.)


aligns: no