A blog about teaching and learning in a maths classroom.

Saturday, 22 May 2010 | 0 Comments

In the NSW Mathematics Syllabus students are to learn about “rounding numbers to a specified number of significant figures” [NS5.2.1].

Having a teacher in the Maths faculty trained in another subject area, has helped us think about how we explain certain topics. “Significant figures” is a good example. Here is my, I think simple, explanation as to why we might round to a certain number of significant figures, rather than just rounding to 1 or 2 decimals places.

Say you had measured the length of an ant, and found it to be 0.0013 metres long. [Aside from the obvious, that you would use another unit of measurement] Ask the question, what numbers in this measurement are *important* or *significant*. If we were to round 0.0013 to 1 or 2 decimal places (0.0 and 0.00 respectively) we lose all the usefulness of this measurement. So, when recording some measurements, we will keep the digits of that measurement that are important, i.e. significant.

You could go with a more complicated explanation, but this simple example, allows you quickly draw an ant on the board, and the students get this simple example.

Posted in • Lesson Idea • Rounding • Significant Figures | Short URL: http://mths.co/1833

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**Simon Job** — eleventh year of teaching maths in a public high school in Western Sydney, Australia.

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