When you use a calculator, you must have a rough idea of the expected size of your answer.
This size is called the order of magnitude and you can get a good idea by rounding off the question first.
7840 × 28 is approximately 8000 × 30 which is 240000
24216 - 18947 is approximately 24000 - 19000 = 5000
542 ÷ 18 is approximately 500 ÷ 20 or 25
Example
Let's find the order of magnitude for 3.42 × 19.
| 3.42 × 19 lies between |
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and |
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| which equal |
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3.42 × 19 lies between 3 × 19 and 4 × 19.
| 3.42 × 19 lies between |
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and |
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| which equal |
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and |
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Check to see how close you are by doing the calculation on your calculator as well.
| 3.42 × 19 = |
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This activity contains 10 questions
