Unit 10 Exploring Addition and Subtraction within 1000

In Unit 10 students will:

  • Mentally add 10 or 100 to a given number 100-900, and mentally subtract 10 or 100 from a given number 100-900.
  • Understand that the three digits of a three-digit number represent the amounts of hundreds, tens, and ones; e.g., 706 equals 7 hundreds, 0 tens, 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).
  • Add and subtract within 1000, using concrete models or drawings and strategies based on place value, properties of operations, and/or relationship between addition and subtraction; relate the strategy to a written method.
  • Understand that in adding or subtracting three digit numbers, one adds or subtracts hundreds from hundreds, tens from tens, ones from ones; and sometimes it is necessary to compose or decompose tens or hundreds.

By the end of Unit 10 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 10.

  • Add and Subtract within 1000

  • Add and Subtract within 1000