First Grade · Math · week 16

Add tens to a number (23+30)

Add a multiple of ten to a two-digit number by adding only to the tens digit.

Adding a tens number like 30 or 50 is friendly -- only the tens digit changes, and the ones digit stays exactly the same. For 23 + 30, the ones digit (3) does not move; only the tens digit grows.

23 has 2 tens; add 3 more tens (from the 30) to get 5 tens. The ones stay at 3. So 23 + 30 = 53.

📋 For the teacher
Teach it (10–15 min):
  • Build the starting number with rods and units, then add only more rods (tens) -- the units pile never moves.
  • Point out that 30 = 3 tens and 0 ones, which is why the ones do not change.
  • Practice going the other direction too: which tens number was added, given the start and end?
  • Connect back to "ten more" from two weeks ago -- adding 30 is just three "ten mores" in a row.
Talk about it:
  • What happens to the ones digit when you add 40 to a number?
  • How is adding 30 like doing "ten more" three times?
  • What is 56 + 20?

Mastery looks like: They add any multiple of ten to a two-digit number by changing only the tens digit.

Common stumbles: Changing the ones digit by mistake; miscounting how many tens are being added.

See it visually

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

AdditionSee groups combine — with counters, blocks, and the number line.try →MultiplicationEqual groups and arrays make products finally click.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.
← Back to todayAll coursesYear planner