Calculating with measurements
Measure, compare, add, and subtract lengths (m/cm/mm), mass (kg/g), and volume/capacity (l/ml) using standard units
What a learner can do afterwards
- Measure a length in centimetres and millimetres
- Weigh an object using grams and kilograms
- Add two measurements in the same unit (e.g. 250 ml + 400 ml = 650 ml)
The lesson
Once you can measure something, you can add or subtract those measurements just like regular numbers. The rule is simple: only add or subtract when the units match, so centimetres go with centimetres, grams go with grams, and millilitres go with millilitres.
Priya adds the two weights: 900 g + 600 g = 1500 g. Since 1000 g make 1 kg, that is the same as 1 kg and 500 g altogether.
Before you add or subtract, check that the units are the same. You cannot add 5 cm and 20 mm without changing units first. Change 5 cm into 50 mm, then add: 50 mm + 20 mm = 70 mm.
Add or subtract measurements only when the units match, and convert first if they do not.
Watch it
Where it sits
Where this leads
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.