Task 6
Difference
See the difference as the physical gap between two lengths and record it compactly.
We do
Place black and orange side by side. Fill the gap to make the black train equivalent to orange. The fitting rod is light green.
The difference between orange and black is light green.
o − k = g
Here the − sign signals that we are looking for the difference between the two lengths. Put the longer rod first.
Repeat with blue and pink:
b − p = y
Your turn — Find the difference
Place each pair side by side. Try to identify the difference by looking, then fill the gap to check.
- blue and pink
- dark green and red
- dark green and light green
- red and white
Record each result using colour letters and an equation.
Show answers
- b − p = y
- d − r = p
- d − g = g
- r − w = w
Feedback / teacher prompts
- Which differences could you see without moving the rods?
- Can different pairs have the same difference?
- Find two pairs with a difference of red; then two with a difference of light green.
Your turn — Same difference
Choose one difference and find as many pairs of rods as you can with that same difference.
Organise your pairs so somebody else can see the pattern.
Can you convince your partner that you have found them all?
What could you change?
Specify the difference and ask for possible pairs, use trains instead of single rods, ask for several pairs with the same difference, predict before touching, or hide one rod and give only the other rod and the difference.
Rehearse the teaching
For a task worth practising, work in pairs. One person teaches while the other responds as a pupil using the rods. Model enough to get the pupil started, then stop explaining and question their thinking. Swap roles.
Reflect: What was harder to explain than you expected? Which wording or question worked well?