Grade 1 Unit of Study 3: Add and Subtract Within 100

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In This Unit of Study…

Students begin by exploring the adding of a two-digit number and a one-digit number with sums to 100 representing quantities of items by using concrete and pictorial models. They will focus on adding tens to tens, ones to ones, and combining 10 ones to form new tens, when needed. These base-10 strategies are the foundation of the place value system. Once they have a good understanding of combining ones and tens, they will move on to adding by using models, drawings, or number lines. Students will also explore subtraction of a one-digit number from a two-digit number by using manipulatives, drawings, or equations to decompose tens and regroup ones, when needed. They will also utilize the number line as a tool to count on or count back.

B.E.S.T. Benchmarks:

  • MA.1.NSO.2.4 Explore the addition of a two-digit number and a one-digit number with sums to 100.
  • MA.1.NSO.2.5 Explore subtraction of a one-digit number from a two-digit number.

Key Concepts:

  • I can use the relationship between addition and subtraction to restate a subtraction problem as a missing addend problem.
  • I can explore the addition of a two-digit number and a one-digit number with sums to 100 using manipulatives, number lines, drawings, or models.
  • I can combine ones and tens and compose new tens from ones when needed.
  • I can explore subtraction of a one-digit number from a two-digit number using a number line.
  • I understand subtraction as an unknown addend problem.
  • I can use manipulatives, drawings, or equations to decompose tens and regroup ones when subtracting.

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