Grade 1Tens and Ones1.NBT.B.2c

Counting by Tens

10, 20, 30 … 90 are 1 ten, 2 tens … 9 tens.

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You know tens and ones. Counting by tens is counting bundles.

6 tens: 10, 20, 30, 40, 50, 60.

Key idea

10, 20, 30 … 90 are 1 ten, 2 tens, 3 tens … 9 tens, with 0 ones.

Why it works

Each ten-stick holds 10 cubes. Counting the sticks by tens counts all the cubes inside them.

Worked example: Seven ten-sticks

How many cubes are in 7 ten-sticks?
  1. Count by tens: 10, 20, 30, 40, 50, 60, 70.
  2. 7 tens is 70.

Answer: 70

Worked example: How many tens?

How many tens make 90?
  1. Count by tens to 90: 10, 20, 30, 40, 50, 60, 70, 80, 90.
  2. That is 9 tens.

Answer: 9 tens

For grown-ups: Count by tens with dimes, bundles of straws, or fingers of different people (each person holds up 10).

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, Grade 1, 1.NBT.B.2c: the numbers 10, 20, 30 … 90 refer to one, two, three … nine tens and 0 ones
  • Institute of Education Sciences practice guide: Assisting Students Struggling with Mathematics: Intervention in the Elementary Grades (WWC 2021006)
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