Significant figures and decimal places

Following the finding that students struggle with significant figures and decimal places, we added a question that tested fairly basic rule-based understanding (of stuff that I thought we were teaching quite well in the Maths for Science book).

The question is shown on the left hand side.

I have to say that I’ve been quite surprised by what it is that students got wrong. You may like to think about what you’d expect before reading on.

Using the variant of the question shown as the example, about 95% of the 300 or so students on the presentation we looked at knew that 0.074 is to 3 decimal places, and 87% knew that 0.074 is to 2 sig figs.

86% knew that 7.20 is to 2 decimal places but only 78% knew that 7.20 is to 3 sig figs. The most common error (in 8.4% of responses) was to give this as 2 sig figs – and an additional 3.5% thought 7.20 was given to 2 sig figs and 1 decimal place.  In other words, students do not appreciate that the final zero is there for very good reason!

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