Number
Rounding up and down
Sometimes we don't need to be exact in numbers and we have
to make sensible measurements.
If you were to measure the length of a field you might not be interested in the
number of centimetres, only how long it is in metres.
For example: a school playing field is 60.35m long. This means that it is 60m and 35cm long: the 35cm does not really count here.
If you were asked how long is it to the nearest metre you would say 60m.
YOU HAVE ROUNDED DOWN THE NUMBER.
We often round to the nearest ten, hundred or thousand
depending upon what we are measuring.
How do we know whether to round up or down?
This is the easy bit.
if the last number is 5 or above we round up
If the last number is less than 5 we round down
Here are some examples
Sam, Rebecca and Craig each get pocket money:
|
Name |
Amount per week |
To the nearest 10p |
To the nearest £ |
|
Sam |
£2.78 |
£2.80 |
£3.00 |
|
Rebecca |
£1. 44 |
£1.40 |
£1.00 |
|
Craig |
£3 39 |
£3.40 |
£3.00 |
So, you see, to the nearest pound, both Sam and Craig get the same amount!
Remember that this is rounding and not exact!
Shops often price their good at £3.99, so you see the £3
and forget the 99p
If we round it up, it becomes £4.00.
Try some of these. You will soon get the hang of it
|
Item |
Cost |
Price to the nearest 10p |
Price to the nearest £ |
Price to the nearest £10.00 |
Price to the nearest £100.00 |
|
Shirt |
£16.56 |
£16.60 |
£17.00 |
£20.00 |
- |
|
TV |
£284.99 |
£285.00 |
£285.00 |
£290.00 |
£300.00 |
|
CD |
£14.34 |
|
|
|
- |
|
Computer |
£1259.39 |
|
|
|
|
|
Doll |
£31.50 |
|
|
|
- |
|
Puzzle |
£9.44 |
|
|
|
- |
|
Book |
£19.28 |
|
|
|
- |
|
Games console |
£149.25 |
|
|
|
|
|
Car |
£4,638.99 |
|
|
|
|
Answers
Here are the answers. How did you do?
|
Item |
Cost |
Price to the nearest 10p |
Price to the nearest £ |
Price to the nearest £10.00 |
Price to the nearest £100.00 |
|
Shirt |
£16.56 |
£16.60 |
£17.00 |
£20.00 |
- |
|
TV |
£284.99 |
£285.00 |
£285.00 |
£290.00 |
£300.00 |
|
CD |
£13.34 |
£13.30 |
£13.00 |
£10.00 |
- |
|
Computer |
£1259.39 |
£1259.40 |
£1259.00 |
£1260.00 |
£1300.00 |
|
Doll |
£31.50 |
£31.50 |
£31.00 |
£30.00 |
- |
|
Puzzle |
£9.44 |
£9.40 |
£9.00 |
£10.00 |
- |
|
Book |
£19.28 |
£19.30 |
£19.00 |
£20.00 |
- |
|
Games console |
£149.25 |
£149.30 |
£149.00 |
£150.00 |
£100.00 |
|
Car |
£4,638.99 |
£4,639.00 |
£4,639.00 |
£4,640.00 |
£4,600.00 |
Just remember, this rounding is also useful when you estimate.
Good Luck