3 significant figures – no wonder students find it difficult!

I’ve never thought about devoting a lesson to significant figures before. Partly because it’s a non-topic and partly because it’s possible to cover this topic through teaching other topics. If I think about it though, a large proportion of my students have had trouble with writing numbers correct to 3.s.f, even the IB and A-Level students.

Anyhow, after looking in the textbooks that the year 10 classes use at my new school, there is a full exercise devoted to significant figures. My first thought was to skip the topic and do what I’ve always done but then I started to think about some of the questions and have come to realise that there’s more to it then I’ve ever realised before.

For example, imagine a student trying to write the numbers below to 3 significant figures.

1) 0.0728

2) 13.03

3) 49999

Definite opportunity for confusion here!

With this in mind, I’ve decided to devote a lesson to it and see how it goes. It could certainly be worth it for all the times in the next four years of their education when they get confused by it.

Here’s the lesson plan and the resources that I’m going to use. I’d massively appreciate some feedback on this  with it being the first time that I’ve ever devoted a lesson to it. (E.g. Should there be more work with number lines?)

45 minute lesson – Lesson Plan

Starter: Introduce the lesson via PowerPoint (only first slide) and use geogebra number line to zoom in on 2 examples.

Main: Get them to work in pairs on a worksheet (questions on front page, answers on the back). They derive their own rules about 3 significant figures. We discuss these rules as a class and write them on PowerPoint slide 2.

Go through the worksheet questions as a class (PowerPoint slides 3 and 4) – randomly pick students to check understanding.

They do questions on last slide whilst I walk around and mark their work.

Plenary: Introduce homework task – Tarsia significant figures puzzle (not made yet).

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This entry was posted in Assessment for Learning, Number and tagged . Bookmark the permalink.

2 Responses to 3 significant figures – no wonder students find it difficult!

  1. Claire Perry says:

    I always like to start a sig fig lesson by talking about a big lottery win:
    If you won £3743627.61….
    What would you tell your mum?
    Probably the full amount

    What about your grandma?
    Possibly rounded to the nearest pound

    Your friends? Teachers? The postman?
    This highlights the idea of rounding to sig figs as a real experience but also the necessity of place value of figures.

    Yes, definitely lots of number lines…

    • Thanks Claire, your message prompted me to insert an intro into why we might want to write a number to a certain number of significant figures. In the end, I opted for a football match attendance (78,568 people) and asked the students what number a newspaper would use for the atendance.

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