Comparing and Ordering Decimals

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Comparing and Ordering Decimals

• When Will I Ever Do That???!!!

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McDonalds Menu.Im Lovin It!!

• Double Cheeseburger .99
• Big Mac Value Meal 4.79
• Chicken McNuggetts Meal 3.80
• Small Drink .99
• McFlurry 1.97
• Salad 4.80
• 2 Cheeseburger Meal 3.70
• Ice Cream Cone .87

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Order Up!Least Expensive to Most Expensive

• Ice Cream Cone .87
• Double Cheeseburger .99
• Small Soft Drink .99
• McFlurry 1.97
• 2 Cheeseburger Meal 3.70
• Chicken McNuggetts Meal 3.80
• Big Mac Value Meal 4.79
• Chicken Salad 4.80

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What Do I Mean Compare Decimals?

• When we compare we use terms such as
• Less than lt
• Greater than gt
• Equal to
• Comparing decimals is similar to comparing whole
  numbers.
• 45lt47
• 150gt105
• When we compare decimals we use place value or a
  number line.

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Place Value
1,000 100 10 1 0.1 0.01 0.001 0.0001

Hundreds
Ones
Thousands
Tens
Tenths
Hundredths
Thousandths
Ten-thousandths
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• Compare Saras score with Dannys score.
• Line Up Decimal Points
• Sara 42.1
• Danny 42.5
• Start at the left and find the first place where
  the digits differ. Compare the digits
• 1lt5
• 42.1lt42.5
• This means Saras score was lower than Dannys
  score.

Relay Race Results
Sara 42.1
Danny 42.5
Ross 42.0
Bethany 40.7
Jacob 46.1
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Lets Try Using A Number Line
Sara 42.1
Danny 42.5
Ross 42.0
Bethany 40.7
Jacob 46.1
42.0
42.1
42.5
Numbers to the right are greater than numbers to
the left. Since 42.5 is to the right of 42.1 we
have 42.5gt42.1
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Annexing Zeros

• This means placing a zero to the right of the
  last digit in a decimal.
• 0.6 0.60
• Although we added a zero, the value of the
  decimal did not change!!
• Annexing or adding zeros is useful when ordering
  a group of decimals.

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Ordering Decimals

• We can order decimals from least to greatest or
  we can order from greatest to least.
• Lets try an example
• Order 15, 14.95, 15.8, and 15.01 from least to
  greatest

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15, 14.95, 15.8, 15.01

• First, line up the decimal points
• 15
• 14.95
• 15.8
• 15.01

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15, 14.95, 15.8, 15.01

• Next, annex zeros so that each number has the
  same number of decimal places
• 15.00
• 14.95
• 15.80
• 15.01

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15, 14.95, 15.8, 15.01

• Finally, use place value to compare the decimals.
  Always start from the left!!
• 15.00
• 14.95
• 15.80
• 15.01
• 14.95, 15, 15.01, 15.8

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One More Example

• Order these numbers from greatest to least
• 35.06, 35.7, 35.5, 35.849

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Rounding Decimal Numbers

• Sometimes close enough is good enough!

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Molly has 16 in her pocket

• She buys
• 3 hotdogs _at_ 1.89 each
• 3 milkshakes _at_ 2.19 each
• 3 Large French fries _at_ 1.79 each

Does she have enough money?
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Gas costs 3.30 per gallon
Im running on empty and I have a 20 gallon tank
on my truck About how much will it cost to fill
up?
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You have one hour to take a 50 question test.
About how much time can you spend on each
question?
Close enough is good enough!
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The rounding poem
Find your number Look right next door 4 or less,
just ignore 5 or more add one more!
Write this poem down in your notes!
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Rounding Whole Numbers
Round 474 to the closest hundred.
474
Find your number
Look right next door
Four or less, just ignore Five or more, add one
more
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474 Rounded to the hundreds becomes 500
Round 474 to the closest 10s
474
Just ignore - 470
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What about decimal numbers
The same rules (and poem) apply!
Round 4.167 to the closest hundredths
4.167
Find your number
Look right next door
4.17
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Remember
If you are asked to round to the nearest
tenth.your answer stops at the tenth place!
Example Round 42.73 to the closest tenth would
be 42.7
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Special Case!Rounding a 9
Round 2.197 to the closes hundredths
Since there is a 9 in the hundredths place
consider the tenth and hundredths together 19
do you leave it at 19 or move it to 20?
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Round 4.95 to the closest tenth
Since there is a 9 in the tenth spot consider
the ones and tenths together should you leave
it at 49 or move it to 50?
4.95 rounded to the nearest tenth is 5.0
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Try these
Round to hundredths
Round to tenths
4.56
4.6
18.784
18.78
5.32
5.3
9.46
9.456
10.00
0.98
1.0
9.997