Estimating and Calculating
| Site: | WelTec Moodle |
| Course: | Learning Services |
| Book: | Estimating and Calculating |
| Printed by: | Guest user |
| Date: | Saturday, 20 April 2024, 7:44 AM |
Description
Activities and strategies to help you estimate and calculate numbers.
Introduction to Rounding
"Balance of Payments Deficit $9,000,000"
"350,000 unemployed"
Newspapers, adverts and television often give information in numbers. However, it is unlikely that the Balance of Payments Deficit is exactly $9,000,000 or the number of unemployed is exactly 350,000.
More likely, the Balance of Payments Deficit is more like a number such as $6,895,481 or $7,132,206. From the readers' or viewers' point of view $7,000,000 is a good approximation. Large numbers are often approximated this way.
This process is called rounding.
Use the arrows to view the activities and examples or click the link below to download a printable guide to estimating and calculating.
Rounding to the Nearest 10
If there is a coat with a price tag reading "$89", you would say that this coat costs around $90.
This is because $89 is closer to $90 than it is to $80, so $90 is a reasonable approximation.
$89 has been rounded up to $90.
![](https://moodle.weltec.ac.nz/pluginfile.php/111277/mod_book/chapter/16164/pricetag.png")
Similarly, if the coat cost $82, you would say that it costs around $80 because it is closer to $80 than it is to $90.
Both of these numbers have been rounded to the nearest 10.
Rounding to the nearest 10 means rounding to 10, 20, 30, 40, etc.
The number will end in 0.
The process of rounding to the nearest 10 is summarised below.
A number ending in 1,2,3 or 4 or less is rounded down; a number ending in 5, 6, 7, 8 or 9 is rounded up.
Practice Questions: Rounding to the Nearest 10
Practice Questions: Check Your Answers
Rounding to the Nearest 100
Remember, to the nearest 10, you have to look at the last digit of the number.
To round to the nearest 100, you have to look at the last two digits.
For example:
267 is nearer to 300 than it is to 200
243 is nearer to 200 than it is to 300
If the last two digits are less than 50 you round down
If the last two digits are 50 or over you round up
Example
The distance from Auckland to Wellington is 649km. Round off the distance to the nearest 100.
649 rounds down to 600.
Therefore, the distance from Auckland to Wellington is approximately 600km.
Practice Questions: Rounding to the Nearest 100
Practice Questions: Check Your Answers
