Idea 22of 23Builds onRounding measurements in real life
Rounded numbers can hide a difference
If two numbers round to the same tenth, are they equal?
Today you'll discover
- how two different masses round the same
- how wide a tenth's rounding stretch is
- when to compare the exact numbers
Think firstTwo pumpkins, both about 3.4 kg
Both pumpkins round to 3.4 kg. Do they have the same mass?
Decide first, then press Next. Read the exact values above the dots.
A number line from 3.3 to 3.5 captioned two pumpkins' masses, with dots A at 3.38 kg and B at 3.42 kg, both moving to 3.4, ringed: both round to 3.4 kg. Then the exact dots alone, then dashed halfway marks at 3.35 and 3.45. The last step shows race times of 12.46 s and 12.54 s.
See the whole ideathe big idea and the key word, in one place
The big idea
Different numbers can round to the same tenth, so compare the exact values, not the rounded ones.
A close race
Ana ran 12.46 s and Ben 12.54 s. Rounded, both are 12.5 s. Exact, Ana was faster by 8 hundredths.
- Ana12.46 s
- Ben12.54 s
Easy to get wrongThat is why races are timed to the hundredth of a second: a tenth is too rough to pick a winner.
Key word
- exact value
- the number as measured, before any rounding
Ready to use it?
- Compare two decimals that round to the same tenth.
- Decide when an exact value is needed.