MAFS.2.NBT.2.8 Mentally add 10 or 100 to a given number 100–900, and mentally subtract 10 or 100 from a given number 100–900.

Cognitive Complexity Level: 1-Recall

[divider] [/divider] Students are able to… 

  • Mentally compute 10 or 100 more or less than any given number and justify their thinking using a variety of materials (concrete/pictorial models, hundreds chart, open number lines).
  • Justify thinking for mental math reasoning about place value and observable patterns.

[divider] [/divider] Students are able to…because teachers:

  • Engage students in problem solving scenarios requiring students to compute 10 or 100 more/less.
  • Strategically sequence learning tasks to build student automaticity with mental math for 10 or 100 more/less.
  • Pose questions and facilitate discussion among students about place value based reasoning.
  • Prepare games and activities where students are given a number and practice finding 10 or 100 more, or 10 or 100 less.

 [divider] [/divider] Questions to ask students:

  • Ask:  What is 100 less than 643?
    • Sample answer that indicates understanding: “543.”
    • Sample answer that indicates an incomplete understanding or a misconception: 633 (Student may be relying on a changing pattern but is not focused in on place value)
  • Ask: How can you use a number line to justify your thinking of 10 more than ___(any given number)?
    • Sample answer that indicates understanding: “I started at ___ and counted on 10 more jumps to ___(correct number that is 10 more).”
  • Ask: Explain the pattern you can use to add or subtract 10 or 100 from any number.
    • Sample answer that indicates understanding: “If I’m adding or subtracting 10 then I can add or subtract one from the number in the tens place. If I’m adding or subtracting 100, then I can add or subtract one from the number in the hundreds place.”

[divider] [/divider] Additional Resources:

Additional in depth content knowledge

http://www.katm.org/flipbooks/2%20FlipBook%20Final%20CCSS%202014.pdf#page=37

Video: Adding 10 or 100

 

[divider] [/divider] Sample Formative Assessment Tasks:

[divider] [/divider] Resources/Tasks to Support Your Child at Home:

  • Kahn Academy Video: Adding 10 or 100
  • Give your child a 3-digit number to represent using virtual base ten blocks. Then ask your child to show 10 or 100 more, or 10 or 100 less. Repeat with different numbers in the range of 100-900.
  • Use the 1-1000 chart to find and discuss patterns when adding or subtracting 10 or 100. Ask your child if they notice which digits stay the same and which digits change when adding and subtracting 10 or 100.