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OUR LESSON : Rounding and

Estimating

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Use > or < to compare these numbers.

1.) 2.35___ 2.33

2.) 3.13___ -3.13

3.) 5.05___ 5.00

4.) 1.01 ___ 1.10

5.) -0.01 ___ -0.001

WARM-UP:

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Lets review what we did in the last lesson

Decimals are numbers which have dot (decimal) in it

Digits of the number to the left of the decimal point represent the whole number

Digits on the right of the point are decimal fractions. If there is no whole number , the decimal will begin with a zero in the units position .

Digits after the decimal point are read individually

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Lets take an example

523 , 52.3 , 5.23 , 0.523 These three numbers above have the same

three digits, in the same order, yet they are very different.

523 is a whole number and would be read as five twenty three.

The second number has a decimal in it and would be read as fifty two point three

5.23 would be read as five point two three 0.523 contains no whole number in it so will

be read as point five two three

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We can also compare two decimals by comparing the digits in each place-value position.

T O . T H TH

4 . 6 4 4 . 5 2

Start at the left and compare the digits in each place- value position.

In the ones place, the digits are the same In the tenths place, 6 > 5, so,

4.64 > 4.57

Comparing Decimals

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We are familiar with Decimals and their place-value

positions.

So now will learn how rounding of decimal numbers is done

to get to the nearest approximate whole number.

It is a kind of Estimation that we make.

We use Rounding to estimate time, money, distances etc.

Lets Get Started

Rounding and Estimation

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Lets try to understand the importance of this concept with this example

If our supermarket bill totals to $52.29 we would give $52 at the counter.

However if the total was $52.85 we would be required to give $53

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Rules of Rounding of Decimals

We can round decimals to any place value.

Find the place value you want (the "rounding digit") and look at the digit just to the right of it.

If that digit is less than 5, do not change the rounding digit but drop all digits to the right of it.

If that digit is greater than or equal to five, add one to the rounding digit and drop all digits to the right of it.

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1) 28,458 2) 28,925 3) 28,512

28,000 29,000 29,000

So lets see how we round these numbers to the nearest thousand.

The rounding Digits are in Red

The digit to their right is in Yellow

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Let us take another example

Round 73,852 to the nearest

1. Ten-thousand.

2. Thousand.

3. Hundred.

4. Ten.

70,000

74,000

73,900

73,850

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Another way that we can round the decimals is to their Nearest Fractions

Lets round 625.3682 to the nearest

1.) Tenth

2.) Hundredth

3.) Thousandth

4.) Last Digit

625.4

625.37

625.368

625.3682

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Now you try some !

1.) 325.34 To the nearest Hundred

2.) 48.722 To the nearest Ten thousand

3.) 43.381 To the nearest Hundredth

4.) 60.528 To the nearest Tenth

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Estimating with Decimals Estimate by Rounding

Example 23.485 – 9.757 23.485 23 9.757 10 23.485 – 9.757 is about 23 -10 = 13 The difference is about 13

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Your Turn! Estimate 43.9 x 37.5 Estimate 6.43 + 2.17 + 9.1 + 4.87

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Lets see how well you have grasped your concept today

Compare and arrange these decimals from least to the greatest after rounding them to the tenth.

82.36, 82.81, 61.83, 61.49, 65.88

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Break Time!!

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GAME TIME click here to play a Game

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1)Write three decimals that would round off to 82.356

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2.) The Grocery bill for Mrs. Johnson is $282.31. What amount is required to be paid by Mrs. Johnson if the bill is rounded to the nearest dollar

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3) The exact distance from the school to the house for five students is given as under

4.53, 6.12, 8.61, 1.28, 3.81

The teacher has asked them to write the distance in a form which has space of only one digit after decimal. What should each student write there?

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1. Round each number to the underlined place-value positiona) 46.124b) 29.915c) 331.98

2. Round each number to the place indicated.a) 0.219; hundredthb) 15.552; tenthc) 9.6; unit

3. Estimate by rounding 432.87 ÷ 8.94. Estimate by rounding 23.84 + 12.13

Assessment

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Let's Review what we have learnt today

Find the place value you want and look at the digit just

to the right of it.

5,834 To the nearest thousandth

If that digit is less than 5, do not change the rounding digit but drop all digits to the right of it.

8 is greater than 5

If that digit is greater than or equal to five, add one to the rounding digit and drop all digits to the right of it so here we get 6000

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RememberWe can also round the decimals to their nearest Fractions

in the same way

Lets round 83. 461 to the nearest tenth place

83.4 6 1

The place value number is 4 and number to its right is 6.

6 Is greater than 5 so

We round the number to 83.5

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You had a GREAT lesson today!

Be sure to practice what you learned!