Cut a round thing for an awkward number. A cake, a pizza, a pancake or a paper plate. Wrap a strip of paper round the edge and measure it. Divide by the number of people. Mark the strip and wrap it back round. Cut from each mark to the very middle. (A grown-up holds the knife with the child.)

Before chapter 4. Is a seventh bigger or smaller than an eighth?

The answer. Bigger. The more equal pieces you cut a whole into, the smaller each piece. An eighth is 0.125, a seventh is about 0.143, a sixth about 0.167. In the book the tin is 63 cm round, so the marks go every 9 cm.

The recipe: a simple plum pie (serves 7). A ready-made pastry case, 6 ripe plums cut into quarters, 3 spoons of sugar, a pinch of cinnamon, 1 spoon of flour. Toss the plums with the sugar, cinnamon and flour. Fill the case. Bake at 190°C (gas 5) for about 35 minutes, until bubbling. A grown-up handles the oven. Cool, then cut into sevenths.

The grown-up layer. Children often think a bigger bottom number means a bigger piece. Placing fractions on a line helps. FractionForge has the number line and the pie.

For the ride home. Ask: how would you share a pizza between three?