Idea 6of 22Builds onBenchmarks for mass and capacity
Could that really be its size?
How can you tell when a measurement must be wrong?
Today you'll discover
- how one number can be three sizes
- how to check with a benchmark
- how to fix the unit
Think firstA worksheet says a pencil is 15 m long
A worksheet says a new pencil is 15 m long. Could that be right?
Decide first, then press Next. Hold each size up to something you know.
A new pencil at the left. Down the right, three lengths it might be: 15 m (taller than 7 doorways), 15 cm (a bit less than a hand span) and 15 mm (less than 2 fingernails wide). The 15 cm line is ringed. The last step shows a pet cat with 4 g, 4 kg and 40 kg.
See the whole ideathe big idea and the key word, in one place
The big idea
Check every measurement against a benchmark: if it could not be that size, something is wrong.
One number, three sizes
The same 15, held up to benchmarks.
- 15 mmunder 2 fingernails
- 15 cmunder a hand span
- 15 mover 7 doorways
Easy to get wrongA number alone is not a measurement. 15 means nothing until you know the unit: 15 mm, 15 cm or 15 m?
Key word
- reasonable
- makes sense when you compare it with the benchmarks you know
Ready to use it?
- Spot a measurement that could not be right.
- Fix its unit.