Choosing units and measuring in two units

In Primary 2, you measured length in metres and centimetres, mass in kilograms and grams, and volume in litres. Today, we will choose suitable units and write measurements in two units. Here is today's question. A ribbon is measured using a metre ruler. Two full metre lengths and another forty-six centimetres cover it exactly. Write its length in metres and centimetres. The ribbon is longer than the metre ruler. First, look at the metre ruler. It is marked from zero to one hundred centimetres. One hundred centimetres make one metre. The ribbon is longer than one metre, so we measure the whole metres first. From the start of the ribbon to the end of the ruler is one full metre. Make a pencil mark where the ruler ends. Slide the ruler along until it starts at the mark. That is another full metre. Mark where it ends again. One metre and one more metre make two metres. Slide the ruler along once more. This time, the ribbon ends before the ruler does. So the last part is shorter than one metre. A part shorter than one metre is measured in centimetres. The question tells us this part is forty-six centimetres. Let's check it on the ruler. Here is the forty mark. Count on: forty-one, forty-two, forty-three, forty-four, forty-five, forty-six. So the extra part is forty-six centimetres. Here it is, under the ribbon. To write the length, we write the bigger unit first: the whole metres. Then we write the extra centimetres. So the ribbon is two metres forty-six centimetres long. The whole metres come first. Mass works the same way: kilograms first, then grams. Volume works the same way too: litres first, then millilitres.

Amara's flask holds one thousand, five hundred millilitres of water when full. Write its capacity in litres and millilitres. Try it first. Pause if you like. Capacity is how much the flask holds when it is full. To write it in litres, we need to know how many millilitres make one litre. One litre is one thousand millilitres. The flask holds more than one thousand millilitres, so it holds more than one litre. So we split off one full litre. One thousand, five hundred minus one thousand is five hundred millilitres. The bottom part is one litre. The top part is the five hundred millilitres left over. So the capacity is one litre five hundred millilitres.

Amara takes a bus to her grandmother's home. The bus trip is about twelve, blank. Choose the most suitable unit: centimetres, metres or kilometres. Try it first. Pause if you like. To choose, think about how long each unit is. One centimetre is about as wide as your fingertip, so we measure a short pencil in centimetres. One metre is one hundred centimetres, about one big step, so we measure a ribbon in metres. One kilometre is one thousand metres, about a fifteen-minute walk or a few bus stops. Now watch the bus trip. Twelve centimetres is about a short pencil, much too short. Twelve metres is about twelve big steps, still much too short. So the bus trip is about twelve kilometres. Twelve kilometres is a long ride, past many bus stops. A measurement in two units gives the whole big units first, then the extra small units.