Math Background

Two-Digit Addition With Regrouping: When Students Ask

  • Will I always regroup when I add?
    Explain to children that they will not always regroup when adding two-digit numbers. Tell them that if the ones add up to 10 or more, they will regroup and put a 1 above the tens column to show the 10. Remind children that they must place the leftover ones under the ones column. Explain that if there are fewer than 10 ones, they will not regroup because they need 10 ones to regroup.
  • How can I add two-digit numbers correctly?
    Explain to children that they need to decide whether they should regroup first. Then, if they need to regroup, they should regroup the ones into a ten and ones. Remind children that it is necessary to record each step as they do it—for example, they write the 1 for the regrouped 10 over the tens column and the leftover ones in the ones column. Finally, when they add the tens column, they should be sure to add the 1 that represents the ten regrouped ones.
  • When do I write zero in the ones column?
    Explain that a zero will be written in the ones column when there are no ones left after regrouping.
  • Why do I need to know this?
    Explain to children that they might need to keep score at a game, or they might need to know how much two things cost at the store or how many miles they have to go to visit two friends, and so on. Also point out that they will add more than two columns as they learn to do more complex math.
  • Why should I know how to estimate a sum?
    Tell children that it is not always necessary to have an exact answer. Point out that when they go to the store, they might need to decide quickly if they have enough money to buy several items. Have children suppose that their class and another class want to go on a field trip, but the bus available to take them holds only 48 children. They can quickly round to the nearest ten and estimate whether there are enough seats on the bus for both classes.

Houghton Mifflin Math Grade 2