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Lauren Petty-Rounding

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Lauren Petty

on 29 April 2016

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Transcript of Lauren Petty-Rounding

Lauren Petty-Rounding

What is "Rounding" ?

Rounding means making a number simpler but keeping its value close to what it was.

The result is less accurate, but easier to use.


Example: 73 rounded to the nearest ten is 70, because 73 is closer to 70 than to 80. But 75 goes up to 80.


Rounding Numbers


Decide which is the last digit to keep
Leave it the same if the next digit is less than 5 (this is called rounding down)
But increase it by 1 if the next digit is 5 or more (this is called rounding up)
Example: Round 74 to the nearest 10

We want to keep the "7" (it is in the 10s position)
The next digit is "4" which is less than 5, so no change is needed to "7"
Answer: 70

(74 gets "rounded down")
How to Round Numbers
Example: Round 86 to the nearest 10

We want to keep the "8"
The next digit is "6" which is 5 or more, so increase the "8" by 1 to "9"
Answer: 90

(86 gets "rounded up")

So: when the first digit removed is 5 or more, increase the last digit remaining by 1.


Another Example


5 is in the middle ... so we could go up or down. But we need a method that everyone agrees to.

So think about sport: we should have the same number of players on each team, right?


0,1,2,3 and 4 are on team "down"
5,6,7,8 and 9 are on team "up"
And that is the "common" method of rounding. Read about other methods of rounding.


First work out which number will be left when we finish.

Rounding to tenths means to leave one number after the decimal point.
Rounding to hundredths means to leave two numbers after the decimal point.
etc.
3.1416 rounded to hundredths is 3.14
as the next digit (1) is less than 5

3.1416 rounded to thousandths is 3.142
as the next digit (6) is more than 5

1.2735 rounded to tenths is 1.3

as the next digit (7) is 5 or more

To round to "so many decimal places" count that many digits from the decimal point:

1.2735 rounded to 3 decimal places is 1.274

as the next digit (5) is 5 or more
Rounding Decimals
We may want to round to tens, hundreds, etc, In this case we replace the removed digits with zero.

134.9 rounded to tens is 130

as the next digit (4) is less than 5

12,690 rounded to thousands is 13,000

as the next digit (6) is 5 or more

15.239 rounded to units is 15

as the next digit (2) is less than 5


Rounding Whole Numbers

Why does five go up?
Full transcript