2.NBT.B.8 - About the Math, Learning Targets, and Increasing Rigor

Full Standard

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

Measurement Topic

This standard is reported on the report card in these quarters as follows:

About the Math

Skills and concepts below are learning goals for this standard.

Students who are forced to rely on algorithms and procedural understanding of mathematics struggle with the ability to fluently add and subtract 10 and/or 100 to numbers. These students often try to rewrite the problem in an algorithmic fashion because they believe that is what they have to do to do math.

• Mentally add 10 to a given number from 100-900.
• Mentally subtract 10 from a given number from 100-900.

Students should first work to understand 10 more and 10 less than 3-digit numbers. This can be done in a variety of ways. Hundred charts and modified hundred charts are good opportunities for this. These tools should be connected to base ten representations so that students can understand which place values change and why when we add or subtract a ten from a number. Students should work with number strings to focus on the patterns within these computations.

• Mentally add 100 to a given number 100-900.
• Mentally subtract 100 from a given number from 100-900.

As students show proficiency with adding and subtracting 10, we can begin to focus on adding and subtracting 100 from a number. Again, use of base ten models will help students understand what is happening mathematically. Then, students should work number strings and related equations to reinforce the patterns within these computations.

Essential vocabulary for this standard includes: tens, hundreds, digit, value, skip count, ones, place, rows & columns (for visualizing hundreds chart), add, subtract, forward, backward, sum, and difference.

Progression of Standard within Grade 2

This progression informs how to develop the standard within the grade level. This progression is provided by HCPSS Elementary Mathematics.

Progression of this Standard Across Grades

This progression is informed by the Achieve the Core Coherence Map Links to an external site.. Information is not the complete standard.

TASKS

These tasks can be used with small group or whole group instruction.

• Distribute either place value dice or digit cards and place value blocks. Have students generate a 2-digit number and create a model using the base ten blocks. Then have students add 10 to their model and record their work in their journal. For example, they could generate the number 24. then add ten more to their model and record 24 + 10 = 34 in their journal. They could repeat this by taking away 10, and by generating a 3-digit number and adding and subtracting 10 or100.
• Display a hundreds chart. Discuss the patterns students see on the hundreds chart.  What do you notice as we look down a column? What do you notice as we look across the rows?
• Distribute a place value mat and place value disks.  Generate a 2-digit number. Have students show you ten more than the number on their place value mats. Record the equation on the board. Repeat this several times and discuss what patterns they notice. This can also be done using a 3-digit number and adding or subtracting 10 or 100.
• Skip count by ten by starting at 10 and counting on. Next, start at a number that is not a multiple of ten such as 8. Additionally they can count backwards starting with a number such as 320 then with 347. As students are counting, record the number stated on the board. Ask questions such as what patterns do you see? Would I say the number 35 when counting? Why or why not? What do you notice about the digit in the tens place when counting by ten and bridging over 100?
• When we add ten to a number, what do you notice about the digit in the tens place?  Does the digit in the hundreds place change? Explain your thinking.
• Add and subtract 10 from 247. What do you notice when looking at the three numbers? What about when you add and subtract 100 from 247?
• Starting at 765, how many groups of ten will you need to add to get to 805? Starting at 329, how many groups of hundred will you need to add to get to 929? (reverse these question types for subtraction)
• How does a hundred chart help you when you are adding and subtracting 10 from a number like 57? (or multiple groups of 10 such as 30 and 50)
• How does a number line help you when adding or subtracting 100 from a number like 432? (or multiple groups of 100 such as 200 or 600)
• Caroline is solving 72 + 10. She is using a hundred chart. She starts on 72 and counts 73, 74, 75, etc. until she gets to 82. Paul says there is an easier way to find the answer using the hundred chart. What do you think Paul will tell Caroline?

SLIDE-BASED TASKS 

  These links are HCPSS created instructional tasks. These tasks are provided in Google slides.  These tasks should be used for inspiration and resources, but instruction should start with students having the opportunity to engage with the math first (often involving physical and/or visual models) followed by discussion and explicit instruction to ensure student understanding.

Additional Tasks 

  These links provide ideas for lessons connected to this standard.

• Comparisons 2 Links to an external site.(Illustrative Math)
• Adding and Subtracting 10s and 100s Download Adding and Subtracting 10s and 100s
  (Utah Core Academy Lesson) 
• Arcade Tickets Download Arcade Tickets
  (Utah Core Academy Lesson)
• Buying a Wii Download Buying a Wii
  (Utah Core Academy Lesson)
• Hungry Cows Download Hungry Cows
  (Utah Core Academy Lesson)
• Sheep Shearing Download Sheep Shearing
  (Utah Core Academy Lesson)
• Shake, Rattle, and Roll Links to an external site. (Georgia Department of Education, pgs. 37-41)
• Where Am I on the Number Line? Revisited Links to an external site. (Georgia Department of Education, pgs. 29-33)

Tasks From Print Resources

  These publications have been provided for each school. They are typically stored in team closets or the media center. Check with your team leader if you cannot find them. 

Print Resources

Book Thumbnail	Book Title	Grade	Pages
	Teaching Student-Centered Mathematics	K-3	139 (More and Less on the Hundreds Chart, Activity 5.11) 139 (Models with the Hundreds Chart, Activity 5.12) 139 (The Thousands Chart, Activity 5.13) 140 (Digit Change, Activity 5.6) 285 (Calculator Skip Counting, Activity 10.9) 288 (Fractured Chart Pieces, Activity 10.12)
	Hands On Standards	3-4	20-21 (Adding and Subtracting, pages 20 - 21
	Nimble with Numbers	1-2	106-107 (Fifty Chart Pieces) 108-109 (Find My Number) 110-112 (What's in that Place) 115-116 (Claim All You Can) 121-122 (Fill in the Pieces)
	Mental Math in the Primary Grades	K-2	49-50 (Skip Counting by 5s, 10s, 100s) 51-52 (Patterns on the Hundred Chart) 53-54 (Tracing Paths on the 100 Chart) 55-56 (Arrow Moves on the 100 Chart) 57-58 (Using the 100 Chart to +/- 10s and 1s) 59-60 (Using the 100 Chart to +/- Multiples of 10)
	Math Intervention: Building Number Power	PK-2	122-124 (Adding and Subtracting Tens)
	Math In Practice Teaching Second-Grade Math	2	Module 4

Centers

  These print resources can be used during independent or center time. These resources could also be used as lesson seeds.

• 4 in a Row (+10) Download 4 in a Row (+10)
  (HPCSS-adapted resource)
• Around the World (-10 V2) Download Around the World (-10 V2)
  (HPCSS-adapted resource)
• Around the World (-10) Download Around the World (-10)
  (HPCSS-adapted resource)
• Around the World (+10) Download Around the World (+10)
  (HPCSS-adapted resource)
• Froggy Jumps of 10 Links to an external site. (HPCSS-adapted resource)
• Minus 10 and Minus 100 Download Minus 10 and Minus 100
  (HPCSS-adapted resource)

INDEPENDENT PRACTICE/HOMEWORK/ASSESSMENT

  These resource sheets can be used for independent practice, homework, or assessment. They are intended to reinforce procedures and concepts. They should not be used as a source of direct instruction or whole-group practice.

• Add and Subtract 10 and 100 Links to an external site.

• Mentally and and Subtract 10 Links to an external site.
• Mentally Add and Subtract 100 Links to an external site.
• Mentally Add and Subtract 10 and 100 (performance task) Links to an external site.
• Mentally Add and Subtract 10 and 100_2 Links to an external site.
• Mentally Add and Subtract 10 and 100_3 Links to an external site.
• Represent 10 More on a Number Line (performance task) Links to an external site.
• Represent 100 More on a Number Line (performance task) Links to an external site.

Full Standard

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

Measurement Topic

The standard is reported on the report card through these measurement topics. Expand the measurement topic for a description of what students who meet expectation are able to do.

2nd Grade Students Learning 2nd Grade Standards by Measurement Topic

1st Grade Students Learning 2nd Grade Standards by Measurement Topic

2NBT8 Anecdotal Data Collection Tool (Addition) Links to an external site.

2NBT8 Anecdotal Data Collection Tool (Subtraction) Links to an external site.

Visit the SBIR (Standards Based Instruction and Reporting) page in Course Essentials for more information and clarification. 

Rubric (for thinking and reasoning evidence)

Use this rubric for observation and constructed responses (tasks that require explanation, justification, and/or representation).

Rubric for Tasks (pdf) Links to an external site.

Exemplars for this standard (if available)

These samples are examples of what it might look like for a student who MEETS EXPECTATIONS, is MAKING PROGRESS, and/or is MAKING LIMITED/NO PROGRESS.