Mathematics Alignment Lesson
Grade 2 Quarter 3 Day 108
Common Core State Standard(s)
2.NBT.8 Mentally add 10 or 100 to a
given number 100-900, and mentally
subtract 10 or 100 from a given number
100-900.
Standards for Mathematical Practice
Standard 2: Reason Abstractly and
Quantitatively
Standard 4: Model with Mathematics
Standard 6: Attend to Precision
Standard 7: Look for and make use of
structure
Standard 8: Look for and express
regularity in repeated reasoning.
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Materials Needed:
Blackline Master, “Mental Math
Gameboard”
Cardstock, “Add or Subtract Game
Cards” (1 per pair of students)
Transparency, “Number Clues”
Baggies
Base Ten Blocks, Secret Code Cards,
100/200 hundred chart (optional)
Sticky Notes
Dice (3 dice per pair of students)
Formative Assessment
- Activity 1: Discussion questions
-Activity 2: Number clues
-Activity 3: Informal observation/notes
-Activity 4: Quick Quiz
Homework
Blackline Master, “Journal Prompt Add
and Subtract 10 or 100 to a 3-digit Number”
Vocabulary
Place value, digit, ones, tens, hundreds,
more, less, add, subtract
Wake County Public School System, 2014
Alignment Lesson
More Mental Math Strategies
*Note: This standard focuses only adding and subtracting 10 or 100 to a 3-digit
number to become proficient mentally, not working in multiples of 10 or 100.
Second grade students should realize that when one adds or subtracts 10 or 100
that only the tens place or the digit in the hundreds place changes by 1. Students
should notice the patterns in place value and connect the digit change with the
amount changed. Students should mentally add or subtract within the same
hundred before crossing hundreds.
Remediate: Ask students to find 10 more or 10 less than a given 2-digit number.
Example (What is 10 more than 82? 10 less than 82?)
Enrich: Ask students to multiples of 10 or 100 to a given 3-digit number.
Example (Add or subtract mentally 20 and 200 from each of the following
numbers: 456, 981, 231, 295)
Activity 1 (ENGAGE and EXPLORE) Guess the Rule (10 min)
1. Write the following set of patterned numbers in a 2-column
chart on the board. Provide wait time for students once all
numbers have been posted in columns of the chart. Allow for
students to turn and talk about the patterns they notice.
231
241
251
261
271
281
291
231
331
431
531
631
731
831
2. Ask for students to guess the rule for sorting the numbers into
the columns. (Rule: +10 in 1st column and +100 in 2nd
column). Discuss in whole group the following questions:
-What is the difference between the place and the value of a digit?
-What happens to the value of a number when we add 10 or 100
to it? What digits change? What digits stay the same? Why?
-How would the numbers in the chart look if we were to subtract
10 or 100? Choose one of the numbers in the chart and subtract
10 and then subtract 100 from it.
-What happens to the value of a number when we subtract 10 or
100 from it? What digits change? What digits stay the same?
Why?
3. Review vocabulary. Choose a 3-digit number to model for
students using place value blocks, secret code cards, or a
100/200 chart to summarize the discussion when using place
value structure of numbers to observe the pattern rule when
adding and subtracting 10 or 100.
Source: Teacher Generated
Lesson Continued on Next Page . . .
Teacher Guide
Grade 2
Day 108
Standard(s) 2.NBT.8
Alignment Lesson
More Mental Math Strategies
Continued
Activity 2 ( EXPLAIN and ELABORATE) Guess the Number- (20 min)
1. Begin this task by instructing students to listen actively as they will be read aloud and shown some number clues. The
number clues progress from easy to challenging.
2. Pass out a sticky note and have students number it 1-6. They will need to write the answers to the clues on the sticky
note.
3. Read aloud and reveal each clue one at a time using Transparancy, “Number Clues”. Ask students to mentally solve
each number clue using a strategy based on place value. Wait until all number clues have been shared before
solutions should be discussed in a whole group.
4. Discuss each of the number clues and use models and tools (place value blocks, hundreds charts, secret code cards)
to reinforce that when one adds or subtracts 10 or 100 that only the tens place or the digit in the hundreds place
changes by 1. Students should notice the patterns in place value and connect the digit change with the amount
changed. ( If students struggled with clues #5-6, they may need more support mentally add or subtract within the
same hundred before crossing over hundreds.)
5. Promote math talk in a whole group discussion by asking other questions to connect and clarify ideas such as: What
did ____just say? Can you tell me more? Who can repeat what _____just said? Does anyone want to add on to
what ____said? Do you agree or disagree with _____’s idea? Is this what you said? Can you prove it? What do you
think will happen if _____? What makes you say that?
6. Allow time for students to write a number clue of their own on the back of the sticky note. Have students pick a 3digit number and write a clue for it including statements about being 10 more/10 less than or 100 more/100 less than.
Have students partner up to share clues or pass clues to someone in the group to solve. For struggling students, have
teacher pull a small group and ask students to work with 2-digit numbers finding 10 more and 10 less. As you scaffold
this standard for students, allow them to use place value blocks, secret code cards, and/or 100 chart.
7.
Activity 3(EXTEND) Guessing Game Add and Subtract 10 or 100 (20 min)
1. Each pair of students will need Blackline Master, “Mental Math Game Board”, 3 dice, a pencil, and a set of
Cardstock, “Add or Subtract Game Cards” .
2. Students play in partners. Each player takes turns rolling 3 dice to create a 3-digit number.
3. Both players record the same number on their “Mental Math Game Board”.
4. Both players then pick a card from the “Add or Subtract Game Cards” and follow the instructions on his/her game
card and then each player records their new number on the game board.
5. Players then share their new number with one another while taking turns guessing how the new number was made
either by adding or subtracting 10 or 100. Both players must check and agree. Variation: Players can share their game
card add/sub 10 or 100 and have the other player guess the new 3-digit number.
Differentiation: Advanced students may choose to create 4-digit numbers and/or add/subtract with multiples of 10 and
100. Early finishers may respond to the journal prompt at the bottom of their game board. Struggling students may only
need to play the game with 2 dice creating 2-digit numbers and/or only working with addition or subtraction of 10 or 100.
Activity 4 (EVALUATE)- Quick Quiz (10 min)
Distribute a sticky note to each student. Have students number it 1-5. Choose a different 3-digit number each time.
Ask students to either add or subtract 10 or 100 from that given number. (Examples: What is 10 more than 532? What
is 100 less than 862? What is 453- 10? What is 498+10? What is 142-100?) Have partners switch sticky notes and
then check the answers. Return to original student for self reflection and then collect the quick quiz.
Students should complete Blackline Master, “Journal Prompt Add and Subtract 10 or 100 to a 3-digit Number” for
homework.
Wake County Public School System, 2014
Blackline Master
Grade 2
Day 108
Standard(s) 2.NBT.8
Mental Math Game Board Add or Subtract 10 or 100
Name: _______________________________Date: ______________________
Actual 3-Digit Number
Roll the dice
Example:
542
Add or Subtract 10 or 100
Pick a game card
New 3-digit Number
Guess your partners
-10
532
Journal Prompt: How do you know that 10 more than 296 is 306? Make a model to prove it. Justify
your thinking using precise vocabulary as you explain it in writing.
Wake County Public School System, 2014
Cardstock Grade 2
Day 108
Standard(s) 2.NBT.8
Add or Subtract Game Cards
+10 +10 +10
-10
-10
-10
-100 -100 -100
+100 +100 +100
Wake County Public School System, 2014
Blackline Master
Grade 2
Day 108
Standard(s) 2.NBT.8
Name:__________________________Date:______________________
Journal Prompt HW
Add and Subtract 10 and 100 to a 3-digit Number
Directions: Choose any 3-digit number. Complete the table to show how you can add
and subtract 10 and 100 from that number. Explain your mental strategies for adding
or subtracting based on place value using precise language and models correctly.
Choose a 3-digit Number __________________
+10
-10
+100
-100
I can add and subtract 10 or 100 mentally because I know __________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________.
________________________________________________________________________________
________________________________________________________________________________
Vocabulary
Place value, digit, ones, tens,
hundreds, more, less, add, subtract
Wake County Public School System, 2014
Transparency Grade 2
Day 108
Standard(s) 2.NBT.8
Number Clues
1. I have 100 more than the number 393. What
number am I?
2. I have 100 less than the number 731. What
number am I?
3. I have 1 ten more than the number 429. What
number am I?
4. I have an 8 in the hundreds place and a 6 in the
tens place and a 1 in the ones place. Subtract 10
less to find out what number I am.
5. I am 1 ten less than the number 405. What
number am I?
6. I have a 2 in the tens place and a 7 in the ones
place and a 9 in the hundreds place. Add 100
more to find out what number I am.
Wake County Public School System, 2014
Answer Key Grade 2
Day 108
Standard(s) 2.NBT.8
Number Clues- Answer Key
1. I have 100 more than the number 393. What number am I? (493)
2. I have 100 less than the number 731. What number am I? (631)
3. I have 1 ten more than the number 429. What number am I? (439)
4. I have an 8 in the hundreds place and a 6 in the tens place and a 1 in the ones place. Subtract
10 less to find out what number I am. (851)
5. I am 1 ten less than the number 405. What number am I?(395)
6. I have a 2 in the tens place and a 7 in the ones place and a 9 in the hundreds place. Add 100
more to find out what number I am. (1027)
Wake County Public School System, 2014