Here is a metre stick and a one-litre jug of water. You already know how to read a scale by counting the equal marks along it. Look at the ten equal marks on the metre stick and the ten equal marks up the jug.
Hands up: where exactly is halfway along this metre stick, and how much water do you think fills the jug halfway up? What part of the whole thing is that halfway mark?
Look at the metre stick marked into ten equal tenths. Each tenth is 10 cm. Look at the mark five tenths along: that is exactly halfway. We can read it three ways, half a metre, five tenths of a metre, 0.5 m, and in centimetres that is 50 cm.
Now look at just the first mark. One tenth of a metre is 0.1 m, and that is 10 cm. The marks show 10, 20, 30 centimetres at one tenth, two tenths, three tenths.
Look at the mark eight tenths along. That is 0.8 m, and counting in tens of centimetres it lands on 80 cm, nearly the whole metre, but two tenths short.
Half a litre is the same idea: five tenths of a litre is 0.5 l, and that is 500 ml.
Now we measure in our groups of four. Each group shares one metre stick and one jug, and everyone takes a turn to point and read. If your group has no metre stick or jug, read the same amounts from the board and mark your copybook edge into ten equal parts.
Take turns to point to and read these amounts, in this order: half a metre, then one tenth of a metre, then half a litre, then three tenths of a metre. Each one is a number of equal tenths — say the tenths aloud, then the centimetres or millilitres.
Finished early? Point to seven tenths of a metre and read it, then work out how many more centimetres would make half a metre from three tenths.
In your maths copy, write half a metre three ways in one line, and half a litre three ways underneath it:
Read each line aloud to yourself after you write it.
Now we take turns at the board and work through these readings together, hardest last: two tenths of a metre (0.2 m), then half a metre (0.5 m), then seven tenths of a metre (0.7 m), then eight tenths of a metre (0.8 m), then half a litre (0.5 l) on the jug. Before each reveal, predict where the mark lands and how many centimetres or millilitres it is.
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