Standard

Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.

Student language:

• "I can add and subtract three-digit numbers."

Explanation

About the Math, Learning Targets, and Rigor

This standard mentions the word fluently when students are adding and subtracting numbers within 100. Fluency means accuracy (correct answer), efficiency (reasonable steps and time in computing), and flexibility (using strategies such as making 10 or breaking numbers apart).

See strategies below as well as the Addition and Subtraction strategy sheets.

Addition strategies based on place value for 48 + 37 may include:

• Adding by place value: 40 + 30 = 70 and 8 + 7 = 15 and 70 + 15 = 85.
• Incremental adding (breaking one number into tens and ones): 48 + 10 = 58, 58 + 10 = 68, 68 + 10 = 78, 78 + 7 = 85
• Compensation (making a friendly number): 48 + 2 = 50, 37 – 2 = 35, 50 + 35 = 85

Subtraction strategies based on place value for 81 - 37 may include:

• Adding up (from smaller number to larger number): 37 + 3 = 40, 40 + 40 = 80, 80 + 1 = 81, and 3 + 40 + 1 = 44.
• Incremental subtracting: 81 -10 = 71, 71 – 10 = 61, 61 – 10 = 51, 51 – 7 = 44
• Subtracting by place value: 81 – 30 = 51, 51 – 7 = 44

Properties that students should know and use are:

• Commutative property of addition (Example: 3 + 5 = 5 + 3)
• Associative property of addition (Example: (2 + 7) + 3 = 2 + (7+3) )
• Identity property of 0 (Example: 8 + 0 = 8)

Note: Students should have experiences solving problems written both horizontally and vertically. They need to communicate their thinking and be able to justify their strategies both verbally and with paper and pencil.

It is vital that student-invented strategies be shared, explored, recorded and tried by others.

Resources

Videos

• Instructional Video (6:18 - 12:29)
• Khan Academy
  • scroll to find 2.NBT.5, click on a skill, watch videos on left side in each skill
• Learn Zillion

EngageNY Lessons

• Add/Subtract within Multiples of 10 (Module 1, Topic B, Lesson 6)
• Add within 100 using properties of addition to make ten (Module 1, Topic B, Lesson 7)
• Decompose to subtract from a 10 (Module 1, Topic B, Lesson 8)

Extra Practice

• North Carolina Tasks
• Illustrative Math Tasks
• Howard County Tasks
  • Click on 2nd grade at bottom, then 2.NBT.5
• Common Core Sheets

Released Assessment Questions

2.NBT.5 Student Example

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