Unit 3 Day 1: What is a Decimal?

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Unit 3: The World of Decimals

Day 1: Understanding the Basics

Where have you seen these before?

$4.99

Price Tag

12:30

Digital Clock

98.6°

Temperature

That little dot is a decimal point. It's a separator!

What is a Decimal?

A decimal is simply another way to write a fraction.

Decimals represent the "parts" or "pieces" of a whole number.

The Star of the Show: The Decimal Point

Its only job is to separate the whole numbers from the fractional parts.

12 . 345

Whole Number Part
(1 or greater)

Fractional Part
(Less than 1)

Decimal Place Value

The places to the right of the decimal all end in "-ths".

Hundreds Tens Ones . Tenths Hundredths
100 10 1 \(\frac{1}{10}\) \(\frac{1}{100}\)

Visualizing Tenths

The first place after the decimal means we split one whole into 10 equal parts.

\(\frac{3}{10}\) = 0.3

"three tenths"

Visualizing Hundredths

The second place means we split one whole into 100 equal parts.

\(\frac{42}{100}\) = 0.42

"forty-two hundredths"

I Do: Reading and Writing Decimals

How do we read and write 1.25?

1.25

1. Read the whole number: "One"

2. Say "and" for the point.

3. Read the rest: "twenty-five"

4. Say the last place value: "hundredths"

"One and twenty-five hundredths"

We Do: Let's Try Together

How do we write 4.8 in words?

\(\rightarrow\) Four and eight tenths

How do we write "Twelve and three hundredths" as a number?

Hint: We need a placeholder zero!

\(\rightarrow\) 12.03

You Do: Practice with a Partner

Try these two problems on your whiteboards.

Problem 1:

Write 16.9 in word form.

Problem 2:

Write "Five and fifty-one hundredths" as a number.

Independent Practice

Try these problems on your own.

Green Level

What is the place value of the 7 in 12.57?

Yellow Level

Write 4.09 in word form.

Red Level

Juan has 2 whole dollar bills and 3 dimes. Write the amount of money he has as a decimal.

Exit Ticket

On a piece of paper, solve these on your own.

1. Write 0.81 in word form.

2. Write "Sixteen and two tenths" as a decimal number.

Unit 3: The World of Decimals

Day 1: Understanding the Basics - Notes

What is a Decimal?

Decimal Place Value

Tens Ones . Tenths Hundredths
10 1 . \(\frac{1}{10}\) \(\frac{1}{100}\)

Visualizing Decimals

Tenths: 0.3 is the same as \(\frac{3}{10}\). We shade 3 parts out of 10.

Hundredths: 0.42 is the same as \(\frac{42}{100}\). We shade 42 parts out of 100.

How to Read and Write Decimals

  1. Read the whole number part.
  2. Say "" for the decimal point.
  3. Read the number to the right of the decimal.
  4. Say the place value of the digit.

Example: 1.25 is "One twenty-five ."

Practice Problems

Write in word form:

16.9 \(\rightarrow\)

Write the decimal number:

Five and fifty-one hundredths \(\rightarrow\)

Exit Ticket

1. Write 0.81 in word form.

2. Write "Sixteen and two tenths" as a decimal number.