First Grade · Math · week 14

Ten more, ten less -- mentally!

Mentally find ten more or ten less than a given two-digit number without counting by ones.

Here is a shortcut: to find ten more than a number, add one to the tens digit and keep the ones digit the same. Ten more than 23 is 33 -- only the tens digit changed!

Ten less works the same way backward: subtract one from the tens digit. Ten less than 56 is 46.

📋 For the teacher
Teach it (10–15 min):
  • Use a hundred chart -- ten more is the number directly below; ten less is directly above.
  • Say it as a rule every time: "only the tens digit moves."
  • Practice mentally, without blocks, once the hundred-chart pattern is clear -- that is the goal skill.
  • Try quick oral rounds, like "ten more than 52?", back and forth for fun.
Talk about it:
  • What happens to the ones digit when you find ten more?
  • On a hundred chart, where is ten less than a number?
  • Can you find ten more than your age plus 20, in your head?

Mastery looks like: They find ten more or ten less than any two-digit number mentally, without counting by ones.

Common stumbles: Changing the ones digit by mistake; counting by ones instead of using the mental shortcut.

See it visually

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

Counting & Ten-FramesCount objects in ten-frames and base-ten blocks, one tap at a time.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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