KCounting to 20K.CC.A.1

Counting to 100 by Ones and Tens

Count by ones and by tens all the way to 100.

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You can count on from any number. Now let’s count all the way to 100! The hundred chart shows every number.

The shaded squares are the tens: 10, 20, 30 … 100. Each row is one more ten.

Key idea

After a number ending in 9 comes a new ten: 29, 30. Counting by tens goes 10, 20, 30 … 100.

Why it works

The ones go 1 to 9, then a new ten starts. The ten words, twenty, thirty, forty and so on, tell which ten you are in.

Worked example: A new ten

What comes after 39?
  1. 39 ends in 9, so a new ten comes next.
  2. After thirty-nine comes forty: 40.

Answer: 40

Worked example: Counting by tens

Count by tens from 10 to 50.
  1. 10, 20, 30, 40, 50.
  2. Each jump is one more ten.

Answer: 10, 20, 30, 40, 50

Common mistake

Getting stuck where the ten changes, saying “twenty-nine, twenty-ten.” After 29 comes 30. On the chart, look at the next square.
For grown-ups: Count to 100 by tens with jumps or claps. Then practice the tricky spots by ones, like 27 to 33 and 57 to 63.

Practice

Pass with 3 right answers, the last 2 in a row. Each right answer earns 1 XP.

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Sources and further reading

  • Common Core State Standards for Mathematics, Kindergarten, K.CC.A.1: count to 100 by ones and by tens
  • Institute of Education Sciences practice guide: Teaching Math to Young Children (NCEE 2014-4005)
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