Understand the Tens and Ones in Two-Digit Numbers

Students will explain what each digit in a two-digit number represents in terms of tens and ones. For example, 47 means 4 tens (40) and 7 ones. Students use base-ten blocks, drawings, and expanded form to show their understanding.

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Grade 1 · Counting and Place Value to 120 · question 1 of 3

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12 rungs. A star at the top.

What is 4 tens + 9 ones?

How it is taught

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A two-digit number has tens and ones.

The left digit tells how many tens.

Read it: 10 ones make a ten

You have 27 cubes. Counting them one by one is slow. 2 tens sit bundled, and 7 ones sit loose.

Bundle every 10 ones into a ten.
Count the bundles as tens: 2 tens.
Count the leftover ones: 7. Read 2 tens and 7 ones as 27.

Counting all 27 cubes from one works, but it is slow, and it gets slower as the heap grows.

Bundles stay together, so you count 2 tens instead of 20 loose cubes.

The left digit of 27 counts bundles of 10; the right digit counts cubes still loose.

The tens digit counts those bundles; leftover cubes are the ones.

Counting the 2 ten-cubes as 2 ones, then saying 2 and 7 make 9.

Each of those 2 cubes is already 10. 2 tens is 20, plus 7 ones is 27.

How many tens are in 12? — 1. Bundle 10 ones at a time: 12 is 1 ten and 2 ones left loose.

47 = 4 tens + 7 ones

Let's discover what the digits in forty-seven really mean.

First, here are four rods. Each rod is a bundle of ten.

Count the rods by tens: ten, twenty, thirty, forty.

Next, we add some single cubes. These are ones.

One, two, three, four, five, six, seven cubes.

Together, the rods and cubes make the number forty-seven.

The four sits in the tens place.

Four in the tens place means four tens — that's forty.

The seven sits in the ones place.

Seven in the ones place just means seven.

Grade 1 · What each digit in 47 means

So forty-seven is forty plus seven.

Forty-seven means four tens and seven ones. Nice work!

What you see

While they climb, your page writes one true line to ask about tonight, and a short note each Sunday.

MayaGrade 3 · Mathematics

Did you know?

A chessboard has 64 squares — share them out between the 8 rows and each row holds exactly 8.

Today’s goal: 1 star — one skill mastered, every rung of its ladder climbed
Climbing now: Divide within 100

An example student.

MayaGrade 3 · Mathematics

Maya earned 2 stars this week — Interpret multiplication as equal groups, which took 6 answers over 3 days before its star landed 3 days ago and Multiply by 6, 7, 8 and 9. Next up: Divide within 100.

An example week.

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Standard

CCSS.1.NBT.B.2

Understand that the two digits of a two-digit number represent amounts of tens and ones

Grade 1

Quoted from the Common Core State Standards.

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What a star here means

A star here is the top of a twelve-rung ladder, in four blocks of equal length — three of facts and one of the skill used in a real question — where a right answer climbs one rung and a wrong one drops back to the start of the block, never below it. The star is kept for good. How we grade

All of Grade 1

This is one rung of 61 in Grade 1 mathematics, in the order they build on each other.

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