Teaching mathematics
Teaching mathematics

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Teaching mathematics

Teaching idea: A giant’s hand investigation

One way to engage learners in working on ratio and proportion is to leave a ‘giant’s handprint’ on the classroom wall for them to find (Figure 16).

The learners are then asked to investigate the question ‘How big must the giant be?’

Note: Week 8 of this course looks at how you might conduct statistical investigations with learners. You might find it useful to read that section before carrying out this investigation in your classroom.

Described image
Figure 16 A giant’s handprint

Activity 12 Reflecting

Timing: Allow 10 minutes
  • a.What do the learners need to know?

  • b.What do they need to find out?

  • c.How does this problem relate to proportion?


The learners will need to measure the ‘giant’s hand’ and use proportion to calculate the size of the giant.

The idea behind this activity is that learners will investigate the proportions found in the human body. One way to do this is to collect data from the whole class, with each learner measuring their hand size (length, width or both) and height. This is a hands-on, practical activity which will help learners to get a sense of what proportionality means.

Whole-class discussions looking at the class data set may draw out some conclusions about the proportional relationship between hand size and height (or other measures: foot size, arm span, etc.). These relationships can then be related to the giant’s hand measurements to calculate the height (and foot size, arm span, etc.) of the giant. Different learners may come to slightly different conclusions, so encourage them to explain their answers. This will help to develop their proportional reasoning.

Note: in exploring the proportions in the human body, you might like to discuss the golden ratio with your learners. This idea was briefly discussed in the Introduction to this week.

Some teaching ideas based around investigating the golden ratio can be found on the Nrich website.


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