3.2 Decimal fractions in the context of measurement  (Page 2/4)

You probably used millimetres(mm) and centimetres (cm) quite often.

Know this!

10 mm = 1 cm

100 cm = 1 metre

1 000 mm = 1 m

1 000 m = 1 km

2.8 Estimate and then measure each thing listed below, and complete the table below:

3. Measuring Capacity (best done outside on the sports field).

Hands on: practical work

You will need: a measuring jug (ask Mum); a syringe, but NO needle (ask the vet!); water and red colouring matter that you put in food (ask Mum); an empty cooldrink tin; an empty milk packet; an empty bucket; a teaspoon; your mug/cup; a baby’s bath and other empty containers of liquid that you find interesting. You may work in groups. Use the above containers to find out how much liquid each item can hold. ESTIMATE first, write down your estimation and then measure the actual amount.

3.1 Write all your answers in the table below.

You probably worked with millilitres and litres here.

Know this!

1 000 ml = 1 litre

3.2 Now put two and a half mℓ of (edible) red colouring matter into a glass of water. (Use the teaspoon or syringe). Stir, and admire the result. Taste it. Does it taste like cooldrink? Discuss. (Some Foundation Phase learners cannot understand this!)

4. Big pieces, small pieces.

Think carefully and put in the correct sign from>;<; =.

4.1 500 g ___________ half a kg.

4.2 62 mm ___________62 cm.

4.3 1 850 mm _____________ 2 m.

4.4 1 kℓ ____________ 900 litres.

4.5 125 mℓ_____________________ 125 litres.

Discuss your answers with a friend or other members of your group. Then try to make up some similar questions to put to the class.

5. Converting units of measurement.

(Think back to Module 2: fractions and decimal fractions).

• Length.

Remember: 100 cm = 1 m

1 000 mm = 1 m

1 000 m = 1 km

Look at the tape measure. Find 25 cm. It looks like quite a long piece (nearly as long as a ruler). But it’s only a part of a metre. We need 100 cm to make 1 metre.

So 25 cm = $\frac{\text{25}}{\text{100}}$ m or (25 ÷ 100) m. Now use a calculator:

25 ÷ 100 =

25 cm =

25 cm are a part (fraction) of a metre.

• Capacity.

Remember: 1 000 mℓ = 1 litre

1 000 litres = 1 kℓ

Look at 750 mℓ of water in a measuring jug. It looks quite a lot, yet it’s only a fraction of a litre. We need 100 mℓ to make a litre.

750 mℓ = $\frac{\text{750}}{\text{1000}}$ litres. Use a calculator if necessary:

750 ÷ 1 000 =

750 mℓ = 0, litres.

• Mass.

Remember: 1 000 mg = 1 g

1 000 g = 1 kg

Hold a kg packet of sugar in your hand.

500 g = 0,____________kg. Use a calculator if necessary.

• Now write down the missing quantities. Then compare your answers with a friend and if necessary, check on a calculator (using division).

a) 125 mm = 0, _________mm