Second Grade · Math · week 15

Adding three numbers at once

Add three 2-digit numbers by adding ones, then tens, regrouping as needed.

Adding three numbers works just like adding two -- add all the ones together first, then all the tens together. You might regroup more than once if the ones add up to a big number.

Stack the numbers so all the ones line up and all the tens line up. Then add straight down each column.

📋 For the teacher
Teach it (10–15 min):
  • Stack all three numbers neatly in a column -- a messy stack is the number one cause of errors here.
  • Add the ones digits two at a time if that is easier (first two, then add the third) rather than trying to add all three at once in their head.
  • Watch closely for sums like 17 or higher in the ones column; they still only carry a single ten, as long as it is under 20.
  • Celebrate this as a grown-up skill -- three-number addition feels like a big step forward.
Talk about it:
  • What is the first thing you add when there are three numbers?
  • How is adding three numbers similar to adding two? How is it different?
  • Can you find a way to check your answer for 24 + 18 + 35?

Mastery looks like: They add three 2-digit numbers accurately, regrouping when the column sums require it.

Common stumbles: Losing track of a digit when adding three numbers in a column; adding only two of the three numbers by mistake.

See it visually

Interactive, spoken-aloud tools that show this idea in motion.

AdditionSee groups combine — with counters, blocks, and the number line.try →
Homework for this lessonType it, write it with a stylus, or print it for pencil & paper.open →
Records attendance + 15 min of Math for this learner.
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