### Pebbles

Place four pebbles on the sand in the form of a square. Keep adding as few pebbles as necessary to double the area. How many extra pebbles are added each time?

### It Figures

Suppose we allow ourselves to use three numbers less than 10 and multiply them together. How many different products can you find? How do you know you've got them all?

### Bracelets

Investigate the different shaped bracelets you could make from 18 different spherical beads. How do they compare if you use 24 beads?

# Colour Wheels

### Why do this
problem?

This activity, included in a month when we are focusing on visualising, challenges pupils to form pattern images in their heads. The problem encourages them to use this imagery to recognise, describe and manipulate pattern. This leads on to opportunities to build up generalisations using words and this links in aspects of arithmetic, (multiples and divisibility).

### Possible approach

You could introduce this activity orally. Start off by asking the group to imagine a wheel with a blue mark painted on the edge and a red mark painted on the opposite edge. Say that you place it on the ground and roll it. Ask them to talk in pairs about what they think they would see on the ground if the paint was still wet. Share ideas amongst the whole group. Encourage learners to describe using just words at first, rather than using pictures or objects.

Once the blue, red, blue, red ... pattern has been established, ask a few questions like "Can you predict the colour of the third/fifth/tenth/hundredth mark?". Give learners plenty of time to think about each question and at this stage, you can allow them to draw/write if they want to. When discussing their responses, encourage clear explanations. Did they have to draw $100$ marks?

You can then go on to the problem as it is written. You may want to continue working orally to start with, but you could always show the children the animations of the wheel/s or have a large disc/cylinder as a prop.

When it comes to drawing their ideas together, look for learners who express their explanations clearly in terms of multiples. Many children will be able to investigate their own wheels and to ask their own questions, and their work would make an impressive display.

### Key questions

What do you notice?
What would the next mark be? How do you know?
You could draw or write down the sequence of colours and number each one. What do you notice?
How can you predict what the marks will be without drawing or writing?

### Possible extension

Challenge the pupils to find wheels that are different but would produce the same patterns when rolled. Alternatively, here is another question learners could pursue: The third mark on a wheel is red and in a line of colours it is found that the 100th mark made by the wheel is also red. How many marks are there on the wheel altogether?

### Possible support

A wheel or cylinder to roll would be helpful for some pupils, or perhaps just a disc of card on which they could draw coloured marks.

The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice. More information on many of our other activities can be found here.
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