Math Background

Two-Digit Subtraction With Regrouping: Tips and Tricks

  • Begin the chapter by relating several different numbers to 10.
    Ask, “Is this number more or less than ten?”
  • Remind children that when they subtract, their answer (difference) should be smaller than the top number in the algorithm.
  • When children use a hundred chart, remind them that they are subtracting tens, so they must count back. Use the saying, “Count back to subtract.”
  • Provide a variety of materials, such as paper clips, beans, craft sticks, and so on, for children to use when regrouping.
  • Children may want to regroup when it is not necessary. Include examples that do not require regrouping and encourage children to look carefully at the ones in every example and ask themselves, “Do I need to regroup?” Emphasize that this question is important every time they subtract two-digit numbers.
  • In the Math Center, have wipe-off markers and laminated tens and ones mats for algorithms available. Children can make up their own problems and have a friend solve them.
  • When children are dismissed for activities, lunch, home, and so on, have them count back as each group leaves.
  • To reinforce regrouping, place number cards for 11 to 60 in the Math Center. Have a child make a number with tens and ones blocks and then have a partner make it another way.
  • Label cards with amounts from 1¢ to 30¢. Give children pennies and dimes for a given amount, such as 66¢. Have each child pick a card and take that many cents away from his or her coins. Repeat with the new amount and a different card. When children are ready, they can record the subtraction sentence.
  • Set up a classroom store in which items are labeled with two-digit prices. Give each child a specific amount of money. Have children take turns buying an item and telling how much they have left.
  • If children can't keep their numbers in alignment, draw a vertical line between the tens column and the ones column or highlight the ones column in yellow.
  • When introducing the rounding of numbers to estimate the difference, hang a number line in the classroom. Highlight all the numbers with five or more ones. Explain to children that they should locate the number on the number line first, look to see which side of the 5 it is on, and then move right or left to the nearest ten.
  • Remind children that when adding or subtracting money, the cent sign is always part of the answer.
  • When using addition to check subtraction, play a game of concentration. Place cards with subtraction problems and their matching addition problems facedown and mixed up. Have children find the matching pairs. Remind children that their answer (difference) and the number they subtracted are the two numbers they add when they check subtraction.

Houghton Mifflin Math Grade 2