Unit 3 Fluency with Addition and Subtraction within 100

In Unit 3 students will:

  • Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.
  • Explain why addition and subtraction strategies work, using place value and the properties of operations.
  • Add up to four two-digit numbers using strategies based on place value and properties of operations.
  • Use addition and subtraction within 100 to solve word problems involving lengths that are given in the same units, e.g., by using drawings (such as drawings of rulers) and equations with a symbol for the unknown number to represent the problem.
  •  Represent whole numbers as lengths from 0 on a number line diagram with equally spaced points corresponding to the numbers 0, 1, 2, ..., and represent whole-number sums and differences within 100 on a number line diagram.
  •  Understand that the three digits of a three-digit number represent amounts of hundreds, tens, and ones; e.g., 706 equals 7 hundreds, 0 tens, and 6 ones. Understand the following as special cases:
    •  100 can be thought of as a bundle of ten tens — called a “hundred.”

    •  The numbers 100, 200, 300, 400, 500, 600, 700, 800, 900 refer to one, two, three, four, five, six, seven, eight, or nine hundreds (and 0 tens and 0 ones).

  • Use addition and subtraction within 100 to solve one- and two-step word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using drawings and equations with a symbol for the unknown number to represent the problem.

 By the end of Unit 3 your child should be able to answer the following questions:

  • How can I use the context of a story problem to write an equation that solves that problem?
  • How do addition and subtraction strategies help me to become more fluent with my facts?
  • Why do the addition and subtraction strategies that I have been taught work and how do they help me?

The following videos explain some of the topics covered in Unit 3:

  • Adding with Place Value Blocks

  • Partial Sums Algorithm

  • Adding Tens

  • Subtracting Tens

  • Subtracting with Place Value Blocks

  • Subtracting on a Hundred Chart

  • Addition with Regrouping

  • Adding 3 or More Numbers

  • Adding on an Open Number Line

  • 2 Digit Subtraction With Regrouping

  • Counting On Strategy for Subtraction

  • Counting Back Strategy for Subtraction

  • To practice your 2 digit addition skills 


  • To practice you 2 digit subtraction skills