Good Afternoon!

Today we will learn aboutROUNDING AND ESTIMATING DECIMALS

Do you remember Place Value position???

3,456.128

Let's review what we learned in the last lesson.

We learned that when we compare decimals, we line up the decimal points.

Then starting with the tenths place and workingfrom left to right, we find the first place thatthe digits differ.

We use these symbols to compare

> greater than< less than= equals

We can also plot decimals on a number line.

If the number of decimal places is not the same forthe 2 numbers, we must add "place holding" zeros.

And finally.....

Terrific! Let's move on to the new lesson

Then, we can line up the decimals and compare.

In order to round decimals, we first needto underline the digit to be rounded.

83.64

For example, if we are to round to the nearesttenth, we underline the digit in the tenths place.

The second step is to look at the digit TO THE RIGHT OF the underlined digit.

83.64

Look here!

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*

If the digit is 4 or less, the underlined digit remains the same.

If the digit is 5 or more, we add 1 to the underlined digit.

Therefore, if we round 83.64 to the nearest tenth,we get.............

83.6 (Keep it the same)

On a number line, we can see that 83.64 is closer to83.6 than it is to 83.7.

83.6 83.783.61 83.62 83.63 83.6583.64 83.6983.66 83.67 83.68

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Let's try another.....

Round 40.458 to the nearest hundredth.

Underline the digit in the hundredths place.

40.458

40.458

The second step is to look at the digit TO THE RIGHT OF the underlined digit.

Look here!

If the digit is 4 or less, the underlined digit remains the same.

If the digit is 5 or more, we add 1 to the underlined digit.

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*

40.458

In this case, the digit to the right of the underlined digit is greater than 5 so...........we add 1 to the underlined digit to round tothe hundredths place.

40.46

If we want to round to the nearest WHOLE NUMBER...

we first must underline the digit in the ones place.

For example, let's round 146.75 to the nearestWHOLE NUMBER.

146.75

We underline the digit in the ones place.

Look here!

And, once again, we look at the digit to the rightof the underlined digit.

If the digit is 4 or less, the underlined digit remains the same.

If the digit is 5 or more, we add 1 to the underlined digit.

*

*

146.75

So, in this case, we add 1 to the underlined digit.

Therefore, if we round 146.75 to the nearestwhole number, we get.......

147

On a number line, we can see that 146.75 iscloser to 147 than it is to 146.

146.00 147.00146.75146.50146.25

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Now, let's round 14.97 to the nearest tenths place.

14.97

Underline the digit in the tenths place and onceagain, look at the digit to the right.

Look here!

If the digit is 4 or less, the underlined digit remains the same.

If the digit is 5 or more, we add 1 to the underlined digit.

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*

14.97In this case, the number 7 is greater than 5 so wehave to add 1 to the underlined digit.

HOWEVER, when we add 1 to the 9, we get 10so we change the 9 to a 0 AND add 1 to the 4 as well.

14.97Change to 0

Change to 5

If we round 14.97 to the nearest tenths place, we get

15.0

On a number line we can see that 14.97 is closerto 15.0 than to 14.9.

14.9 15.014.91 14.92 14.93 14.94 14.95 14.96 14.97 14.98 14.99

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Let's practice....

1.) Round to the nearest tenth. 65.76

2.) Round to the nearest whole number. 76.43

3.) Round to the nearest hundredth. 123.567

4.) Round to the nearest tenth. 45.09

5.) Round to the nearest hundredth. 6.698

We often use ESTIMATION when we wantto approximate a reasonable sum or difference.

For example, if we purchase 4 items at the storethat cost $3.98, $6.08, $2.85, and $1.25 .....we can estimate the sum by rounding to thenearest whole dollar.

$3.98$6.08$2.85$1.25

round to$4.00$6.00$3.00$1.00$14.00

We estimate that our purchase will cost about$14.00

It is easy to add or subtract decimalswhen we round to the nearest whole number.

EXAMPLE: 24.2 - 5.3 = ?

We can estimate by rounding.....

24 - 5 = 19

Let's practice a few.....

4.2 + 1.76 =

7.8 + 1.126 =

12.1 - 7.05 =

Estimate:

BREAK

GAME

1.) Write three different decimals that round to 12.0 when

roundedto the nearest tenth.

2.) Can you round this decimal to the

nearest thousandth?

45.6998

3.) How many numbers are there that

round to 67.45?

Assessment

1.) Round to the nearest tenth. 4.455

2.) Round to the nearest hundredth.16.089

3.) Round to the nearest whole number.199.42

4.) Round to the nearest thousandth. 67.0099

5.) Round to the nearest tenth. 72.96

6.) Estimate: 0.25 + 0.83 =

7.) Estimate: 3.6 + 7.1 =

8.) Estimate: 102.05 + 6.8 + 0.3 =

9.) Estimate: 50.321 - 4.7 =

10.) Estimate: 0.7 - 0.8365 =

You did a wonderful job today!Let's review what we learned.

In order to round decimals, we first needto underline the digit to be rounded.

The second step is to look at the digit TO THE RIGHT OF the underlined digit.

If the digit is 4 or less, the underlined digit remains the same.

If the digit is 5 or more, we add 1 to the underlined digit.

1.

2.

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*

If the underlined digit is a 9 and we needto round it "UP", we change the 9 to a 0 and add 1 to the digit to the LEFT of 9.

Example: Round 4.98 to the tenths place. 5.0

We often use ESTIMATION when we wantto approximate a reasonable sum or difference.

We can ESTIMATE by rounding to the nearestwhole number.

You worked hard today!

Congratulations!!!