Rounding:
N1
We round numbers to make them easier to
work with.
Nearest 10:
1. When the units are five or higher ….
HIGH FIVE
…… and round up.
Example: 18
20
2. When the units are less than five….
…… round down.
Example: 14
10
Similarly to round to nearest 100 look at the tens digit
and apply the same rule, and to round to nearest
1000 look at the hundreds digit and apply same rule
etc.
Prep 6 Ms Lizanne
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3. Rounding to the nearest whole number
N1
84.5 lies between 84 and 85 and it is exactly
halfway between them. Therefore in this
situation round up. So, 84.5 rounded to the
nearest whole number is 85.
84
84.5
85
4. Rounding prices:
Imagine that you are rounding a price of
€9.54 - to the nearest whole it is €10 while to
the nearest tenth it is €9.50 (as 4 is less than 5)
and so we round down.
5. Counting decimal places (nearest tenth, nearest
hundredth and nearest thousandth).
Decimal places are counted from the
decimal point:
6.127
Prep 6 Ms Lizanne
So, the number 6.127 has
three decimal places; 7.3128
has four decimal places and
6.17 has two decimal places.
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N1
Important:
Therefore: To round a number to a given
number of decimal places, look at the number
in the next decimal place.


If it's less than 5 round down
If it's 5 or more, round up
Note that:
To round a number to a given number of
decimal places then the answer must have
that number of decimal places, even if you
have to add some zeros.
For example, rounding 6.70045 to two decimal
places gives 6.70 (2 d.p.) and not 6.7, even
though the value is equal.
You need to write both decimal places, even
though the second number is a zero, to show
you rounded to two decimal places.
Prep 6 Ms Lizanne
Page 3