Math Background

Modeling and Recording Subtraction: When Students Ask

  • Why should I learn subtraction?
    Lead children to see that subtracting saves time in finding how many crackers are left after you eat some; how many days, weeks, or months are left until you go on vacation; or how many baby teeth you have left after you lose one.

    Explain to children that knowing how to subtract will help them learn how to do more complex math later on.

  • Why do I need to learn the minus and equals signs?
    Explain to children that the mathematical symbols tell you what to do in a number sentence. Whenever they see the minus sign, they will know that they need to subtract. Discuss other signs or symbols, such as stop signs, traffic lights, and danger signs, which children instantly recognize and understand. Explain that mathematical symbols are part of a language that everyone understands and that the symbols and numbers are the same worldwide so people can communicate mathematically even if they speak different languages.
  • How do I know where to put each number in a subtraction sentence?
    Review the meaning of each symbol with children. Remind them that since the minus sign (−) means “subtract,” the number you are subtracting from goes before the minus sign and the number being subtracted goes after the minus sign. Since the equals sign (=) tells you that two amounts are the same, you need to write the difference between the two groups after the equals sign.
  • How do I know when to add and when to subtract?
    Review words and terms such as in all, altogether, and sum, which indicate addition. Remind children that whenever they need to combine groups they need to add. Make sure children recognize the plus sign and know that it means “add.” Similarly, review terms such as take away, how many are left, and difference, which indicate subtraction. Remind children that whenever they need to take away from a group, they need to subtract. Make sure children recognize the minus sign and know that it means “subtract.”

Houghton Mifflin Math Grade K