Here is a real job: we have 12 Maths books to pack, each one 24 cm tall, and a box that is 60 cm tall. Before we work anything out, the first skill today is choosing the right measuring instrument. Ask yourself: are we finding a length or height, a mass, or how much liquid? Length or height means a ruler, mass means a weighing scale, and liquid means a measuring jug. For these books and this box we need heights, so the instrument is the ruler. We read both heights off the ruler first, then we can think about the calculation. What is the very first thing we need to know?

Your teacher works three real problems on the board. Each one works the same way: read the two measurements first, then do one calculation. When two measurements are in different units, we change one first so they match. There are 1,000 grams in every kilogram (1 kg = 1,000 g) and 1,000 millilitres in every litre (1 l = 1,000 ml). Look for what the calculation tells you, and watch the unit stay on the answer.