Math Background

Adding and Subtracting Two-Digit Numbers and Money Amounts: When Students Ask

  • How do I subtract 2 two-digit numbers?
    Demonstrate to children that they can use basic subtraction facts to help them solve two-digit subtraction exercises. First, they subtract the ones and write the answer below the line in the ones place. Then they subtract the tens and put the answer below the line in the tens place. Explain the other methods for subtracting, such as mental math, using paper and pencil, and using base-ten blocks.
  • How is adding and subtracting money like adding and subtracting two-digit numbers?
    Explain to children that adding and subtracting money is like adding and subtracting other numbers. Instead of thinking of tens and ones, they can think of dimes and pennies. They just have to remember to write their answers with the cents symbol (¢).
  • Why would I use addition to check subtraction?
    Help children to understand that it is always best to check their answers after they've completed an exercise. Remind them that because addition and subtraction facts are related, they can use addition to check their subtraction. By checking answers they can be sure that they are correct.

Houghton Mifflin Math Grade 1