Quick shopping puzzle. A shop sells two bottles of water side by side. One label says 0.5 litres. The other label says 0.50 litres. A customer thinks she's being tricked — one must hold more than the other. The shopkeeper says they hold the same amount. Who is right? And while we're at it: a price tag reads €1.05. What would happen if we rubbed out that little zero?

Look at four numbers already on the place-value mat. The columns at the top are U for units, t for tenths and h for hundredths. Each big flat is 1, each rod is one tenth, each small cube is one hundredth. Read each number aloud as you look at it.

Example 1: 0.3 (three tenths)

Three rods in the tenths column. No flats, no small cubes.

Example 2: 0.27 (twenty-seven hundredths)

Two rods and seven small cubes. Two tenths and seven hundredths together make twenty-seven hundredths.

Example 3: 1.05 (one and five hundredths)

One whole flat, no rods, five small cubes. The empty tenths column is doing important work: it holds the place.

Example 4: 2.30 (two and three tenths)

Two flats and three rods. The hundredths column is empty — and 2.30 is the same number as 2.3.

Your turn at the board. We'll build a few more decimals together: when a number is called out, one of you comes up to drag the blocks into the U, t and h columns, and the rest of us check the build out loud before we agree.