Lesson 1

Tens and Ones

Est. Class Sessions: 1

Daily Practice and Problems

Teacher Notes
X

TIMS Bit

Students can solve these problems in many ways. For example, to subtract 31 − 2, begin with 31 and count back 2, “30, 29.”

To subtract 40 − 38, begin with 38 and count up 2, “39, 40.” Let students describe their strategies and discuss the advantages and disadvantages of the different strategies.

  1. 17
  2. 29
  3. 20
  4. 2
  5. 3
  6. 2
  7. Possible strategy: Count backwards from 51 to 49.

A. Subtraction: Counting Strategies

Do these problems in your head. You can use the number line to help you solve the problem.
Write only the answers.

  1. 20 − 3 =
  2. 31 − 2 =
  3. 100 − 80 =
  4. 40 − 38 =
  5. 11 − 8 =
  6. 51 − 49 =
  7. Explain your strategy for solving Question F.