When you use a calculator, it's a good idea to have a rough idea of the expected size of your answer, so that you can see if you've made a mistake!
This size is called the order of magnitude and you can get a good idea by rounding off the question first.
7,840 × 28 is approximately 8,000 × 30 which is 240,000
24,216 - 18,947 is approximately 24,000 - 19,000 = 5,000
542 ÷ 18 is approximately 500 ÷ 20 = 25
Example
Let's find the order of magnitude for 3.42 × 19.
| 3.42 × 19 lies between |
|
and |
|
||
| which equal |
|
and |
|
3.42 × 19 lies between 3 × 19 and 4 × 19.
| 3.42 × 19 lies between |
|
and |
|
||
| which equal |
|
and |
|
Check to see how close you are by doing the calculation on your calculator as well.
| 3.42 × 19 = |
|
There's quite a lot to think about here, but you can always check back to this page by clicking on the red button.
Let's have a go at some questions now.
This activity contains 10 questions
