Level UpStart free trial

1st Grade · 1.NBT.B.2

Tens and ones in 1st grade

Tens and ones is how 1st graders learn what the two digits of a number mean. In 46, the 4 means 4 tens, which is 40, and the 6 means 6 ones. This idea is called place value, and your child builds on it every time a sum gets bigger.

What the standard says

The official Common Core wording, quoted exactly. The plain version follows.

1.NBT.B.2 Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases:

  • 1.NBT.B.2.a 10 can be thought of as a bundle of ten ones – called a "ten."
  • 1.NBT.B.2.b The numbers from 11 to 19 are composed of a ten and one, two, three, four, five, six, seven, eight, or nine ones.
  • 1.NBT.B.2.c The numbers 10, 20, 30, 40, 50, 60, 70, 80, 90 refer to one, two, three, four, five, six, seven, eight, or nine tens (and 0 ones).

What it means, in plain words

A ten is a bundle of ten ones. Picture 10 straws held together with a rubber band. Once the straws are bundled, your child can count the bundle as one ten instead of ten loose straws.

Place value tens and ones means that each digit has a job, and its place decides the job. In a two-digit number, the left digit counts tens and the right digit counts ones. So 37 is 3 tens and 7 ones. The numbers from 11 to 19 are one ten and some ones: 16 is 1 ten and 6 ones. The numbers 10, 20, 30 and so on up to 90 are tens with 0 ones: 60 is 6 tens and 0 ones.

In class, children use base-ten blocks: a long rod stands for a ten and a small cube stands for a one. Tens and ones in 1st grade is mostly about building numbers with these blocks and saying what each digit is worth.

Your child should be able to:

  • Explain that 10 ones make one ten
  • Say how many tens and ones are in any two-digit number
  • Build a two-digit number with bundles of ten and loose ones
  • Tell what each digit is worth, for example that the 6 in 64 means 60

Example

How many tens and ones are in 71, and what is each digit worth?

  1. The left digit is 7, so there are 7 tens.
  2. 7 tens is 70.
  3. The right digit is 1, so there is 1 one.
  4. 71 is 7 tens and 1 one, which is 70+170 + 1.

Example

You have 1 bundle of ten straws and 9 loose straws. How many straws is that?

  1. The bundle is 1 ten, which is 10 straws.
  2. The 9 loose straws are 9 ones.
  3. 1 ten and 9 ones make 19.
  4. There are 19 straws in all.

Where children usually get stuck

  • Your child reads 41 as "fourteen", or builds 41 with 1 rod and 4 cubes.

    In the teen numbers, the ones are said first: "fourteen" starts with the 4. The child expects the digits to follow the same order as the words, and in 41 they do not.

    What helps. Build 14 and 41 side by side with straws or blocks. Ask which one has more bundles of ten.

  • Asked what the 8 in 85 is worth, your child says 8.

    The child names the digit, not what it stands for. The 8 sits in the tens place, so it means 8 tens, which is 80.

    What helps. Cover the 5 with your finger and ask how many tens are left. Then count by tens on fingers together: 10, 20, 30 and on up to 80.

  • After bundling straws into tens, your child unties the bundles and counts every straw one by one.

    The child does not yet trust that a bundle always holds ten. Counting by ones feels safer.

    What helps. Count one bundle together to check that it holds ten. Then count the bundles by tens, and count the loose straws last.

Try four practice questions

Real 1st grade questions from our question bank, easiest first. Answer them right here, check each one, and see a worked solution for any question.

  1. 1Warm-up
    A number is made from some tens and some ones.
    Description:
    2 tens and 4 ones\displaystyle \text{2 tens and 4 ones}
    Type the number.
    Show the answer and how to solve it

    Answer. 24

    The number is 24, because 2 tens is 20 and 4 ones is 4, and 20+4=2420 + 4 = 24.

    1. 1Look at the description. It says 2 tens and 4 ones.
    2. 22 tens means 2 groups of ten. Count by tens: 10, 20. That is 20.
    3. 3Now add the 4 ones to 20.
    4. 4The number is 24. The 2 is in the tens place and the 4 is in the ones place.

    Common mistake. A common mistake is to swap the digits and type 42 instead of 24. The tens part of the description comes first, so the tens digit (2) goes in the tens place, and the ones digit (4) goes in the ones place.

    The idea underneath. In a two-digit number, the first digit shows how many tens, and the second digit shows how many ones. The order of the digits tells you the value of the number.

  2. 2On level
    What is the value of the red digit?
    52\displaystyle \textcolor{red}{5}2
    A
    50\displaystyle 50
    B
    5\displaystyle 5
    C
    2\displaystyle 2
    D
    52\displaystyle 52
    Show the answer and how to solve it

    The value of the red 5 is 50 because the 5 is in the tens place. A digit in the tens place tells how many tens, and 5 tens equals 50.

    1. 1Look at the red digit. The 5 is on the left, in the tens place.
    2. 2The 5 is in the tens place. That means 5 tens.
    3. 35 tens equals 50. So the value of the red 5 is 50.

    Common mistake. A common mistake is saying the value of the red 5 is just 5. The 5 is in the tens place, so it stands for 5 tens, not 5 ones. 5 tens equals 50.

    The idea underneath. In a two-digit number, the digit on the left is in the tens place and tells how many tens. The digit on the right is in the ones place. The same digit can stand for very different values — a 7 in the tens place is 70, but a 7 in the ones place is just 7.

  3. 3On level
    Maria wrote four equations for the number 34. Select the correct equation.
    A
    34=\displaystyle 34 = {}
    3+\displaystyle 3 + {}
    4\displaystyle 4
    B
    34=\displaystyle 34 = {}
    30+\displaystyle 30 + {}
    5\displaystyle 5
    C
    34=\displaystyle 34 = {}
    20+\displaystyle 20 + {}
    4\displaystyle 4
    D
    34=\displaystyle 34 = {}
    30+\displaystyle 30 + {}
    4\displaystyle 4
    Show the answer and how to solve it

    Maria's correct equation is 34=30+434 = 30 + 4, because the 33 in 3434 stands for 33 tens (which is 3030) and the 44 stands for 44 ones.

    1. 1Look at the number 34. The 3 is in the tens place, and the 4 is in the ones place.
    2. 2The 3 in the tens place means 3 tens, which equals 30. The 4 in the ones place means 4 ones, which is just 4.
    3. 3Add the tens value and the ones digit:
    4. 4So Maria's correct equation is:

    Common mistake. A common mistake is using the digit 33 instead of its place value 3030. The 33 in 3434 is in the tens place, so it means 33 tens, or 3030 — not just 33.

    The idea underneath. Each digit's value depends on its place. The 33 in 3434 isn't just 33 — it's 33 tens, or 3030.

  4. 4Stretch
    Find the missing number.
    000‾+3=73\displaystyle \underline{\phantom{000}} + 3 = 73
    A
    73
    B
    7
    C
    80
    D
    70
    Show the answer and how to solve it

    The missing number is 70. The 7 in 73 is in the tens place, so its value is 70. That makes 73=70+373 = 70 + 3.

    1. 1Look at the equation. The number on the right is 73.
    2. 2The number 73 has 7 tens and 3 ones. The 7 is in the tens place, so its value is 70.
    3. 3The equation already shows 3 in the ones part. So the blank must be the tens part: 70.

    Common mistake. A common mistake is writing 7 instead of 70. The 7 in 73 is the tens digit, but its value is 70 because it sits in the tens place.

    The idea underneath. Two-digit numbers can be split into tens and ones. The number 73 means 7 tens (which is 70) and 3 ones.