lesson
Choose a unit that fits the quantity
1 · Learn
Metric prefixes connect units by powers of ten: 1 km is 1,000 m, 1 m is 100 cm and 1 kg is 1,000 g. Write the relationship before deciding whether to multiply or divide.
Converting square or cubic units is different from converting lengths because two or three dimensions change. Approximate imperial conversions must be labelled approximate, not treated as exact definitions.
2 · Worked example
2.45 km = 2,450 m. Using the rough comparison 5 miles about 8 km, 15 miles is about 24 km; the result remains an approximation.
3 · Your turn
Convert 3.08 kg to grams and 475 cm to metres. Using 5 miles about 8 km, estimate 10 miles in kilometres.
Check your answer
3,080 g; 4.75 m; about 16 km.
4 · Apply your learning
Choose suitable units for a pencil, a journey and a bag of flour, explaining the choice.
Adult guidance and safety
Ask the learner to explain the method and check it using a different representation. Supply place-value grids, fraction strips, accurate diagrams and measuring tools where needed. These examples need varied practice; a short correct answer alone does not establish fluency.
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Check a calculation · Year 5 onward
Use this only when your teacher or adult allows a calculator for the task. Show your thinking first. It does not replace mental or written arithmetic and does not mark your lesson answer.
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